KR102753062B1 - Laminated film - Google Patents

Abstract

The present invention aims to provide a laminated film having both high transparency and sharp cut property of wavelength, and is a laminated film in which an A layer mainly composed of a thermoplastic resin A and a B layer mainly composed of a thermoplastic resin B different from the thermoplastic resin A are alternately laminated in 51 or more layers, wherein when linearly polarized light (X wave) vibrating in the direction of film orientation is irradiated over a region of a wavelength of 300 to 900 nm and the horizontal axis is plotted as the wavelength (nm) and the vertical axis as the transmittance (%), the transmission spectrum obtained is referred to as the transmission spectrum X, and when linearly polarized light (Y wave) vibrating in a direction perpendicular to the direction of film orientation is irradiated over a region of a wavelength of 300 to 900 nm and the horizontal axis is plotted as the wavelength (nm) and the vertical axis as the transmittance (%), the transmission spectrum obtained is referred to as the transmission spectrum Y, and among the regions surrounded by the transmission spectrum X and the transmission spectrum Y, the area Amax (nmㆍ%) of the largest region is The laminated film is 150 to 1500 in thickness.

Description

Laminated film

The present invention relates to a laminated film having optical properties of spectral shiftability.

Light-cutting films that block light of a specific wavelength band are used in a wide range of fields for the purpose of preventing deterioration of the internal environment or components of applied products due to environmental factors such as light or heat. Representative examples include heat-cutting films for suppressing indoor temperature increases in construction materials and automobiles, ultraviolet-cutting films for absorbing excess ultraviolet rays during ultraviolet laser surface processing in industrial materials, and blue-light-cutting films for shielding blue rays harmful to the eyes emitted from display light sources in the electronic information field. In addition, light-cutting films are used in other fields such as food, medicine, agriculture, and ink for the purpose of suppressing photodeterioration of contents.

As a method for shielding light of a specific wavelength band, there are methods utilizing light absorption (such as adding a light absorber), light reflection, and both thereof. Generally, a method of adding a light absorber to a resin constituting a film (Patent Document 1) is used.

Meanwhile, a method using light reflection (patent document 2) can be achieved by a laminated structure in which multiple resin layers having different refractive indices are laminated, and by precisely controlling the refractive indices of the resin layers, the layer thickness of each layer, the number of layers, and the distribution of the layer thickness, a steep wavelength cut that cannot be achieved by a method of adding a light absorber can be realized.

In order to complement the respective shortcomings of light absorption and light reflection, a combined prescription is used in which a light absorber specialized for light absorption of a wavelength within a reflection wavelength band is added to a film having a laminated structure (Patent Documents 3, 4, 5). By this prescription, the end of the absorption wavelength band is steepened by the effect of light reflection, while the cut wavelength band has sufficient light cuttability due to the effect of the light absorber. In addition, by the effect of increasing the optical path length due to multiple interference reflections derived from the laminated structure, the addition concentration of the light absorber can be greatly reduced. In addition, by the presence of multiple interfaces in the laminated film, bleed out of the added light absorber can also be suppressed.

Japanese Patent Publication No. 2013-210598 Japanese Patent Publication No. 2015-533222 Japanese Patent Publication No. 2013-511746 Japanese Patent Publication No. 2016-215643 International Publication No. 2016/148141

However, it is known that the method disclosed in Patent Document 1 causes the light absorber to bleed out near the nozzle or the vacuum vent during film forming, depending on the type or amount of the light absorber added. If bleed out occurs, it causes a deterioration in film quality, such as film defects due to contamination in the film forming process and a deterioration in cut performance due to a decrease in the light absorber content concentration. In addition, while the light absorber can sufficiently satisfy the cut property within the absorption wavelength band, the absorption wavelength band tends to become broad due to the influence of the molecular structure or side chains that serve as the basic skeleton, so it is often difficult to pinpoint and sharply shield light in a specific wavelength band.

In addition, while the method disclosed in Patent Document 2 is characterized by a steep wavelength cut at a specific wavelength, a cut omission occurs within the reflection wavelength band, making it difficult to completely cut the wavelength across the entire band. In addition, when the visible light region is included in the reflection band, there is a problem that light reflected on the front surface is strongly visible, causing coloring.

When the purpose is to cut the wavelength near the boundary between the visible light range and the invisible light range (ultraviolet range or near-infrared range) by utilizing reflection by a laminated structure, the reflection band shifts slightly due to the influence of a change in the thickness of the laminated film, so when the reflection band shifts and falls on the visible light range, the irradiated light is regularly reflected on the front surface of the laminated film, causing a problem in that the laminated film appears strongly colored by the reflected light. As a method for covering the influence by the reflection band shift, a method of adding a light absorber capable of absorbing light in the range affected by the reflection band shift can be exemplified, however, dyes and pigments, which are light absorbers capable of absorbing light in the visible light range, are not suitable for use as light cut films because pigments have broad absorption bands and dyes exhibit sharp absorption, while they have weak light resistance.

The purpose of the present invention is to provide a laminated film having high transparency and excellent light cuttability, which utilizes the effect of light reflection by a laminated structure and combines the steep cuttability of light in a specific wavelength range and the suppression of coloring by reflected light.

The present invention comprises the following composition:

A laminated film in which 51 or more layers of an A layer containing a thermoplastic resin A as a main component and a B layer containing a thermoplastic resin B different from the thermoplastic resin A as a main component are alternately laminated, wherein when linearly polarized light (X wave) vibrating in the direction of film orientation is irradiated over a wavelength range of 300 nm to 900 nm and the horizontal axis is plotted as the wavelength (nm) and the vertical axis is plotted as the transmittance (%), the transmission spectrum obtained is referred to as the transmission spectrum X, and linearly polarized light (Y wave) vibrating in a direction perpendicular to the direction of film orientation is irradiated over a wavelength range of 300 nm to 900 nm and the horizontal axis is plotted as the wavelength (nm) and the vertical axis is plotted as the transmittance (%), the area Amax (nmㆍ%) of the largest region among the regions surrounded by the transmission spectrum X and the transmission spectrum Y is 150≤Amax≤1500.

The laminated film of the present invention is strongly oriented in an arbitrary direction, and by utilizing the spectral shift property expressed by the strong orientation, it becomes possible to provide a laminated film having steep cut properties and low reflection color (high transparency) even when targeting a specific wavelength range. In addition, since a laminated film in which the orientation is aligned throughout the laminated film plane is obtained, even when irradiated with linearly polarized light, the occurrence of rainbow color spots derived from a two-axis stretched film using a crystalline resin can be reduced, and high transparency and good visibility are obtained.

Figure 1 is a schematic diagram showing a spectral transmission spectrum when a laminated film exhibiting spectral shiftability is irradiated with either X-wave or Y-wave linear polarization.
Figure 2 is a schematic diagram showing an area Amax surrounded by a transmission spectrum X and a transmission spectrum Y.
Figure 3 is a schematic diagram showing another form of the area Amax surrounded by the transmission spectrum X and the transmission spectrum Y.
Figure 4 is a schematic diagram showing a method for calculating an area Amax surrounded by a transmission spectrum X and a transmission spectrum Y.
Figure 5 is a schematic diagram showing an area Amax _{350 to 500} surrounded by a transmission spectrum X and a transmission spectrum Y in a wavelength range of 350 nm to 500 nm.
Figure 6 is a schematic diagram showing another form of an area Amax _{350 to 500} surrounded by a transmission spectrum X and a transmission spectrum Y in a region of a wavelength of 350 nm to 500 nm.
Figure 7 is a schematic diagram showing the cutoff wavelength λ in the transmission spectrum.
Figure 8 is a schematic diagram showing another form of the cutoff wavelength λ in the transmission spectrum.

Hereinafter, the laminated film of the present invention will be described in detail.

The present inventors have found that, for the above-mentioned problem, by strongly orienting the laminated film in an arbitrary direction, a spectrum shift property is exhibited in which the reflection bands can be different in the orientation direction and the direction perpendicular to the orientation direction. By utilizing this feature, the light cut property obtained by irradiating polarized light vibrating in the orientation direction and the direction perpendicular to the orientation direction becomes steeper than in the case of irradiating natural light. In addition, since the light reflected on the front surface of the laminated film is not polarized light but natural light, a color corresponding to the spectrum obtained by averaging each spectrum obtained by irradiating polarized light vibrating in the orientation direction and the direction perpendicular to the orientation direction is recognized as the reflection tone. Therefore, even when the target wavelength band is designed to span the visible light region and the invisible light region, it becomes possible to reduce the reflection color while having a sharp light cut derived from the light reflection design, and a good light cut film that suppresses coloring can be obtained.

In addition, by strongly stretching in a specific direction to express spectral shiftability, the orientation direction of the resin can be made uniform across the film stretching direction, and when polarized light is irradiated, by aligning the irradiation direction of polarized light and the orientation direction of the laminated film, it is also possible to reduce rainbow color spots, which is an essential issue of crystalline biaxially stretched films.

The laminated film of the present invention is a laminated film in which 51 or more layers are alternately laminated, an A layer mainly composed of a thermoplastic resin A and a B layer mainly composed of a thermoplastic resin B different from the thermoplastic resin A, wherein when linearly polarized light (X wave) vibrating in the film orientation direction is irradiated over a wavelength range of 300 nm to 900 nm and the horizontal axis is plotted as the wavelength (nm) and the vertical axis is plotted as the transmittance (%), the transmission spectrum obtained is referred to as the transmission spectrum X, and when linearly polarized light (Y wave) vibrating in a direction perpendicular to the film orientation direction is irradiated over a wavelength range of 300 nm to 900 nm and the horizontal axis is plotted as the wavelength (nm) and the vertical axis is plotted as the transmittance (%), the area Amax (nmㆍ%) of the largest region among the regions surrounded by the transmission spectrum X and the transmission spectrum Y is 150≤Amax≤1500.

The thermoplastic resin A and the thermoplastic resin B used in the laminated film of the present invention include, for example, polyolefin resins represented by polyethylene, polypropylene, poly(1-butene), poly(4-methylpentene), polyisobutylene, polyisoprene, polybutadiene, polyvinylcyclohexane, polystyrene, poly(α-methylstyrene), poly(p-methylstyrene), polynorbornene, and polycyclopentene, polyamide resins represented by nylon 6, nylon 11, nylon 12, and nylon 66, ethylene/propylene copolymer, ethylene/vinylcyclohexane copolymer, ethylene/vinylcyclohexene copolymer, ethylene/alkylacrylate copolymer, ethylene/acrylic methacrylate copolymer, ethylene/norbornene copolymer, ethylene/vinyl acetate copolymer, propylene/butadiene copolymer, Copolymer resins of vinyl monomers, such as isobutylene/isoprene copolymers, vinyl chloride/vinyl acetate copolymers, acrylic resins, such as polyacrylate, polymethacrylate, polymethyl methacrylate, polyacrylamide, and polyacrylonitrile, polyester resins, such as polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and polyethylene-2,6-naphthalate, polyether resins, such as polyethylene oxide, polypropylene oxide, and polyacrylene glycol, cellulose ester resins, such as diacetyl cellulose, triacetyl cellulose, propionyl cellulose, butyryl cellulose, acetyl propionyl cellulose, and nitrocellulose, biodegradable polymers, such as polylactic acid and polybutyl succinate, and other polyvinyl chloride. Polyvinylidene chloride, polyvinyl alcohol, polyvinyl butyral, polyacetal, polyglucolic acid, polycarbonate, polyketone, polyether sulfone, polyether ether ketone, modified polyphenylene ether, polyphenylene sulfide, polyether imide, polyimide, polysiloxane, tetrafluoroethylene resin, trifluoroethylene resin, trifluorochloride ethylene resin, tetrafluoroethylene-hexafluoropropylene copolymer, polyvinylidene fluoride, etc. can be used. One type of these thermoplastic resin may be used alone, or may be used as a blend of two or more types of polymers or a polymer alloy. By performing a blend or alloy, it is possible to obtain properties that cannot be obtained from a single type of thermoplastic resin. Among these, from the viewpoints of strength, heat resistance and transparency, it is particularly preferable to use a polyester resin, and as the polyester resin, a polyester resin obtained by polymerization from a monomer whose main components are an aromatic dicarboxylic acid or an aliphatic dicarboxylic acid and a diol is preferable.

Here, examples of the aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, and 4,4'-diphenylsulfonedicarboxylic acid. Examples of the aliphatic dicarboxylic acids include adipic acid, suberic acid, sebacic acid, dimer acid, dodecanedioic acid, cyclohexanedicarboxylic acid, and their ester derivatives. Among these, terephthalic acid and 2,6-naphthalenedicarboxylic acid are preferable. These acid components may be used alone or in combination of two or more, and furthermore, some oxyacids such as hydroxybenzoic acid may be copolymerized.

In addition, examples of the diol component include ethylene glycol, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene glycol, 2,2-bis(4-hydroxyethoxyphenyl)propane, isosorbate, spiroglycol, and the like. Of these, ethylene glycol is preferably used. These diol components may be used alone or in combination of two or more.

Among the above polyester resins, it is preferable to use a polyester resin selected from among polyethylene terephthalate and copolymers thereof, polyethylene naphthalate and copolymers thereof, polybutylene terephthalate and copolymers thereof, polybutylene naphthalate and copolymers thereof, polyhexamethylene terephthalate and copolymers thereof, and polyhexamethylene naphthalate and copolymers thereof.

The thermoplastic resin B in the laminated film of the present invention must be different from the thermoplastic resin A. Being different from the thermoplastic resin A specifically means that the refractive index is different from the refractive index of the thermoplastic resin A by 0.01 or more in any of two orthogonal directions arbitrarily selected within the plane of the film and the direction perpendicular to the plane. By alternately laminating resins having different refractive indices, it becomes possible to exhibit optical interference reflection capable of reflecting light of a specific wavelength from the relationship between the difference in refractive index and the layer thickness between each layer. In addition, the wavelength (λ) of the reflected light is roughly determined by equation (1) based on the layer thickness of the laminated thermoplastic resins and the difference in refractive indices between the thermoplastic resin A and the thermoplastic resin B, and the reflectance (R) is roughly determined by equation (2) based on the difference in refractive indices between the thermoplastic resin A and the thermoplastic resin B. When thermoplastic resins having the same refractive index are used as thermoplastic resin A and thermoplastic resin B, the numerator of equation (2) becomes 0, especially for light incident in the direction perpendicular to the plane, which means that interference reflection does not occur at the interface between thermoplastic resin A and thermoplastic resin B.

(n _A and n _B represent the refractive indices of thermoplastic resin A and thermoplastic resin B, respectively, and d _A and d _B represent the layer thicknesses of each layer. θ _A and θ _B represent the incident angles when light is incident from layer A to layer B, and the incident angles when light is incident from layer B to layer A, respectively, when viewed from the plane direction of the laminated film. k is an arbitrary natural number.)

As a combination of thermoplastic resins that can be preferably used in the laminated film of the present invention, it is preferable that the difference in the absolute value of the solubility parameter (SP value) of thermoplastic resin A and thermoplastic resin B is 1.0 or less. Since the compatibility of both thermoplastic resins is good, it becomes difficult for delamination to occur at the resin interface when laminated. More preferably, it is a combination in which both thermoplastic resins have the same basic skeleton. The basic skeleton described here refers to a repeating unit of the chemical structure that mainly constitutes the resin, and for example, when polyethylene terephthalate is used as the thermoplastic resin A, in order to realize high-precision lamination of the resins of each layer constituting the laminated film, it is preferable that the thermoplastic resin B contains ethylene terephthalate having the same skeleton as polyethylene terephthalate. In particular, when it is composed of resins that have different optical properties but include the same skeleton, optical interference reflection is available, the lamination precision is high, and delamination at the lamination interface does not occur.

In order to obtain a resin having the same skeleton but different properties, it is preferable that the polymer be a copolymer resin. For example, when the thermoplastic resin A is polyethylene terephthalate, this is an embodiment in which a resin is used as the thermoplastic resin B, which is configured to include a repeating unit formed by including an ethylene terephthalate unit and a dicarboxylic acid component or diol component capable of forming an ester bond as an auxiliary component. The dicarboxylic acid component or diol component contained as an auxiliary component is preferably added in an amount of 5 mol% or more with respect to the dicarboxylic acid component or diol component of the thermoplastic resin to be added in order to express different properties. On the other hand, since the interlayer adhesion of the laminated film or the difference in thermal flow characteristics is small, it is preferably 45 mol% or less in terms of excellent thickness precision and thickness uniformity of each layer. More preferably, it is 10 mol% or more and 40 mol% or less.

When a thermoplastic resin having a polyethylene terephthalate skeleton is used as the thermoplastic resin, preferable components as the copolymerization component include cyclohexanedimethanol, bisphenol A ethylene oxide, spiroglycol, isophthalic acid, isosorbide, cyclohexanedicarboxylic acid, diphenic acid, decalic acid, naphthalenedicarboxylic acid, polyethylene glycol 2000, m-polyethylene glycol 1000, m-polyethylene glycol 2000, m-polyethylene glycol 4000, m-polypropylene glycol 2000, bisphenylethylene glycol fluorene (BPEF), fumaric acid, acetoxybenzoic acid, etc. Among them, it is preferable to use spiroglycol or 2,6-naphthalenedicarboxylic acid. Since spiroglycol has a small difference in glass transition temperature from polyethylene terephthalate when copolymerized, it is difficult to become over-stretched during molding, and delamination also rarely occurs between layers. 2,6-naphthalenedicarboxylic acid is a compound in which two benzene rings are bonded, and it is linear and has higher planarity than terephthalic acid, and has a high refractive index, so it is preferable in terms of increasing light reflectivity.

In the present invention, the term "alternately laminated" means that the thermoplastic resin A constituting the A layer and the thermoplastic resin B constituting the B layer are laminated in a regular arrangement in the thickness direction, and refers to a state in which the resins are laminated according to a regular arrangement of A(BA)n (n is a natural number) or B(AB)n (n is a natural number). In the case of forming a laminated film having a configuration of A(BA)n (n is a natural number) and B(AB)n (n is a natural number), a plurality of thermoplastic resins of the thermoplastic resin A and the thermoplastic resin B are sent out from different paths using two or more extruders, and a known lamination device such as a multi-manifold type feed block or a static mixer can be used. In particular, in order to efficiently obtain the configuration of the present invention, a method using a feed block having fine slits is preferable for realizing high-precision lamination. When forming a laminated film using a slit type feed block, the thickness of each layer and its distribution can be achieved by changing the length or width of the slit to incline the pressure loss. The length of the slit refers to the length of the comb portion that forms a path for alternately flowing the A layer and the B layer within the slit plate.

When the configuration is A(BA)n (n is a natural number), in the laminated film of the present invention, it is preferable that the thermoplastic resin A arranged in the outermost layer is a thermoplastic resin exhibiting crystallinity. In this case, it is preferable because the laminated film can be obtained in the same film forming process as a film having a single-film configuration mainly composed of a thermoplastic resin exhibiting crystallinity. When the thermoplastic resin A is an amorphous resin, when the laminated film is obtained using the general biaxial stretching method described later, there may occur problems such as poor film forming due to adhesion to manufacturing equipment such as rolls or clips, or deterioration of surface properties. In addition, when a crystalline polyester is used as the thermoplastic resin A, since the difference in refractive index Δn in the orientation direction, the direction perpendicular to the orientation direction, and the refractive index in the cross-sectional direction exhibits a large numerical value, it becomes possible to impart sufficient strength and high reflectivity to the laminated film.

The laminated film of the present invention is required to be formed by alternately laminating 51 or more layers of an A layer mainly composed of a thermoplastic resin A and a B layer mainly composed of a thermoplastic resin B different from the thermoplastic resin A. By alternately laminating thermoplastic resins A and thermoplastic resin B having different refractive indices, it is possible to exhibit optical interference reflection capable of reflecting light of a specific wavelength determined by the relationship between the difference in refractive indices of each layer and the layer thickness. By designing with 51 or more layers, a relatively high reflectivity can be obtained over a targeted range in the reflection wavelength band, but furthermore, as the number of layers increases and the number of thickness distributions corresponding to the reflection wavelength increases, reflection over a wide wavelength band or a higher reflectivity can be realized, so that a laminated film that cuts light of a desired wavelength band with higher precision depending on the number of layers is obtained. The number of layers of the laminated film is preferably 100 or more, more preferably 300 or more, and even more preferably 700 or more. In addition, there is no upper limit to the number of layers, but as the number of layers increases, the manufacturing cost increases due to the enlargement of the manufacturing device, and handling properties deteriorate due to the thicker film, so in reality, the practical range is 5,000 layers or less.

The laminated film of the present invention can add a light absorber to any of the thermoplastic resins constituting the laminated film, as will be described in detail later. The light absorber is often a low-molecular-weight component having a molecular weight of less than 1000, and there are cases where the light absorber precipitates or volatilizes (bleeds out) on the surface during the film-forming process or in a long-term durability test after film-forming. By adding it to a layer located in a more inner layer (for example, in the case of a thermoplastic resin B having a configuration of A(BA)n (n is a natural number), volatilization can be physically suppressed by the laminated structure, but in the case of a low number of laminated layers, it is sometimes impossible to completely prevent bleed out. By using a laminated film having 51 or more layers, the light absorber is captured inside the layer due to the presence of the interface between each layer, and precipitation on the film surface can be suppressed, resulting in an optical film suitable for long-term use.

The laminated film of the present invention is characterized in that the transmission spectra obtained when the laminated film is separately irradiated with linearly polarized light (X wave) vibrating in the film orientation direction and linearly polarized light (Y wave) vibrating in a direction perpendicular to the film orientation direction are different (Fig. 1). The orientation direction of the laminated film is mainly affected by the size of the stretching ratio in the long-side direction and/or the width direction in the biaxial stretching direction described later, but since it exhibits complex behavior due to the temperature distribution or shrinkage behavior in the stretching, heat treatment, and cooling processes, it cannot be said that the stretching direction (long-side direction, width direction) and the orientation direction of the laminated film are uniformly identical. Therefore, in the present invention, the direction (long-side direction) in which the refractive index measured from the irradiated light (wavelength 590 nm) is the highest is determined as the orientation direction using the optical parallel Nicol rotation method. In addition, in cases where a measurement result is not obtained due to reflection of light having a wavelength of 590 nm by the laminated film, the alignment direction may be determined by appropriately selecting a wavelength that is not reflected among wavelengths of 480 nm, 550 nm, 630 nm, and 750 nm. Specifically, the determination is made using a phase difference measuring device (KOBRA-21ADH) manufactured by Oji Keiki Co., Ltd., with the film width direction as the angle standard, and the direction matching the numerical value of the obtained orientation angle is defined as the film alignment direction. At this time, the clockwise direction is defined as the + direction, and the alignment direction is expressed as a numerical value greater than or equal to -90° and less than 90°. At this time, the more the laminated film is oriented in the long side direction, the larger the orientation angle numerical value (the absolute value of the numerical value of the orientation direction). In the in-plane phase difference measurement using the phase difference measuring device, the direction indicated by the numerical value of the obtained orientation angle is defined as the film orientation (X-axis) direction, and the direction within the film plane perpendicular to the orientation direction is defined as the Y-axis direction. And, the linear polarization obtained by extracting light that vibrates only in the X-axis direction is defined as X-wave, and the linear polarization obtained by extracting light that vibrates only in the Y-axis direction is defined as Y-wave.

Linear polarization refers to light that vibrates in a specific plane direction including the direction of vibration of an electric field, extracted from natural light, which is an electromagnetic wave that vibrates uniformly in an arbitrary direction. In the laminated film of the present invention, since the spectrum in a state where linear polarization is irradiated is important, linear polarization extracted from natural light emitted from a light source through a linear polarizer in a spectrophotometer is used. Typical linear polarizers include polyvinyl alcohol (PVA)-iodine alignment films, Polaroid (registered trademark), polarizing Nicol prisms, and the like, but in the present invention, linear polarization obtained through a Glenn-Taylor polarizing prism (MGTYB20) made by Karl Lambrecht, Inc., attached to a spectrophotometer U-4100 made by Hitachi High-Tech Science Co., Ltd. is used.

In the laminated film of the present invention, when a linearly polarized X wave vibrating in the film orientation direction is irradiated over a wavelength range of 300 nm to 900 nm and the horizontal axis is plotted as the wavelength (nm) and the vertical axis is plotted as the transmittance (%), the transmission spectrum obtained is referred to as the transmission spectrum X, and when a linearly polarized Y wave vibrating in a direction perpendicular to the film orientation direction is irradiated over a wavelength range of 300 nm to 900 nm and the horizontal axis is plotted as the wavelength (nm) and the vertical axis is plotted as the transmittance (%), the area Amax (nmㆍ%) of the largest area among the areas surrounded by the transmission spectrum X and the transmission spectrum Y is required to be 150≤Amax≤1500.

In the case of a stretched film exhibiting crystallinity, since the crystalline segments of the resin are arranged in the orientation direction, the refractive index tends to increase, and the refractive index decreases in the direction perpendicular to the orientation direction within the plane or in the thickness direction due to recoil. In this case, since the in-plane refractive index changes depending on the direction of the irradiated polarization, the difference between the in-plane refractive index in the polarization direction corresponding to the polarization irradiated surface and the refractive index in the thickness direction differs depending on the direction of the irradiated polarization, and the interference reflected wavelength expressed by Equation (1) also slightly differs. Due to this refractive index difference, a phenomenon occurs in which the wavelength of the interference reflected light shifts in the orientation direction and the direction perpendicular thereto (spectrum shift property). By utilizing this spectrum shift property, when irradiating polarization vibrating in a specific direction, the transmission spectrum can be arbitrarily selected by changing the bonding direction of the laminated film within the range of the transmission spectrum X obtained by irradiating a polarization X wave vibrating in the orientation direction and the transmission spectrum Y obtained by irradiating a polarization Y wave vibrating in a direction perpendicular to the orientation direction.

The spectral shiftability, which is the greatest feature of the present invention, is expressed by a region surrounded by two transmission spectra, namely, a transmission spectrum X obtained by irradiating a polarized X wave vibrating in the film orientation direction, which has the largest spectral shift amount, and a transmission spectrum Y obtained by irradiating a polarized Y wave vibrating in a direction perpendicular to the film orientation direction. The transmission spectrum here refers to a transmission spectrum obtained by 10-point averaging of transmittance data obtained by measuring at a pitch of 1 nm using a spectrophotometer, as described in the measuring method described later. As described in detail later, in the measurement using the spectrophotometer, transmittance data of 295 nm to 905 nm are measured, and transmittance data of 300 nm to 900 nm are obtained by averaging 10 consecutive points of data.

The area surrounded by two transmission spectra is specifically expressed as the area Amax (nmㆍ%) of the largest area among the areas surrounded by both transmission spectra when the transmission spectra X and the transmission spectra Y are plotted on a coordinate where the horizontal axis is wavelength (nm) and the vertical axis is transmittance (%) (Figs. 2 and 3). When there is an area surrounded within the measurement wavelength range, as in Fig. 2, the area surrounded by both transmission spectra is defined as Amax. On the other hand, when there is an area surrounded in a form exceeding the measurement wavelength range, as in Fig. 3, the part of the surrounded area that is included within the measurement wavelength range is defined as Amax. The area Amax of the largest area is approximated by the trapezoidal method. Fig. 4 shows a schematic diagram of the calculation method. The area surrounded by the intersection is divided into 1 nm sections, and the area of the surrounded area is calculated according to Equation (3) for the X-wave transmittance on the short-wavelength side (referred to as wavelength n [nm]) as T' _n , the Y-wave transmittance as T _n , and the X-wave transmittance on the long-wavelength side (referred to as wavelength n+1 [nm]) as T' _{n +1 and the Y-wave transmittance as T n+1} .

Among the regions surrounded by both transmission spectra, if the area Amax of the largest region is less than 150, in one aspect, this means that the difference in the orientation direction of the laminated film and the orientation in the direction perpendicular thereto is small, and since the transmission spectrum does not change significantly even when the polarization state is in any direction, this is against the present concept. In another aspect, in a configuration in which a light absorber is added to the laminated film, there is a case in which the reflection band overlaps the absorption band of the light absorber. In this case, even if a sufficient orientation difference is obtained, the reflection wavelength bands of both spectra are covered by the shadow of the absorption band, which is against the concept of the present invention that utilizes the cutness due to interference reflection.

Among the regions surrounded by the transmission spectra on both sides, if the area Amax of the largest region is greater than 1500, the degree of dependence on the orientation of the constituent resin is large, but since the difference in the orientation of the laminated film between the orientation direction and the direction perpendicular thereto needs to be significantly large, the laminated film is generally obtained by uniaxial stretching, but this is not desirable because problems occur in the film forming process or the product itself, such as inability to obtain a sufficient product width having uniform performance, easiness of tearing in the stretching direction, and significant deterioration of thickness unevenness due to stretching or reflection band unevenness in the plane accompanying therewith. In order to obtain appropriate spectral shiftability while maintaining good film forming properties, Amax is preferably 300 ≤ Amax ≤ 1000.

In the laminated film of the present invention, it is preferable that at least a part of the Amax exists in a wavelength band of 350 nm or more and 500 nm or less. Furthermore, it is preferable that the Amax (Amax _{350 to 500} ) (see Figs. 5 and 6) in the wavelength band of 350 nm or more and 500 nm or less is 150≤Amax _{350 to 500} ≤1500. By targeting the spectral shift property to a wavelength band of 350 nm or more and 500 nm or less, it is possible to achieve a reduction in the reflection color tone of the laminated film requiring cutability between the invisible light region (ultraviolet region) and the blue visible light region, and colorless, transparent, and steep light cut.

Meanwhile, the spectral shiftability, which is a feature of the laminated film of the present invention, can also be applied to the boundary between the red visible light region and the near-infrared region. In this case, by irradiating polarization in a direction perpendicular to the orientation direction, the transmission spectrum Y, which is located on the short-wavelength side among the shifted transmission spectra, becomes a form that cuts near the boundary between the red visible light and the near-infrared light, thereby achieving both reduction of red reflection color and near-infrared region cutability.

For example, in the case of targeting a high-energy visible light (HEV) region of about 350 nm to 400 nm in wavelength, which is required to be shielded in display applications or polarizing eyeglass lens applications, when irradiating with a polarized X wave that vibrates in the film orientation direction, if the design is such that the wavelength of the region can be sharply cut, natural light passing through the polarizing plate of the display or the polarizing film of the eyeglass lens is converted into a polarized X wave having a transmission spectrum X by passing through the laminated film, so that components that are normally affected by HEV, such as display display elements or the macula in the eye, can be protected. In addition, since the laminated film does not exhibit spectrum shift properties with respect to external light, which is natural light, the reflection performance is determined based on the transmission spectrum Z obtained by averaging the transmission spectrum X and the transmission spectrum Y, and therefore, it exhibits colorless transparency rather than the reflection color assumed from the transmission spectrum X. From these features, the laminated film is preferably used in display applications or polarizing eyeglass lens applications.

In addition, when targeting blue visible light (blue light) with a wavelength of 400 nm to 500 nm, since the reflection band shifts toward the long wavelength side, the blue light is reflected more strongly on the front surface due to interference reflection, so the reflection color becomes stronger, but by utilizing the spectrum shiftability, which is a feature of the present laminated film, it is possible to reduce the intensity of the reflected blue color while sharply cutting the blue light. It is more preferable that Amax is _{350 to 500,} 300 ≤ Amax _{350 to 500} ≤ 1000.

In the laminated film of the present invention, it is preferable that the optical density at a wavelength of 390 nm of the transmission spectrum Z obtained by averaging the transmission spectrum X and the transmission spectrum Y is 1.0 or more. The optical density described here is calculated using the numerical value at a wavelength of 390 nm of the transmission spectrum measurement according to equation (4). Since the transmission spectrum Z is a transmission spectrum obtained by averaging the transmission spectra X and Y obtained by mutually orthogonal polarizations, it exhibits properties comparable to a transmission spectrum obtained by irradiating natural light. By exhibiting an optical density at a wavelength of 390 nm of 1.0 or more, it is preferable that a laminated film targeting a high-energy visible light (HEV) wavelength band in the vicinity of a wavelength of 350 nm or more and 400 nm or less or blue light particularly protects components affected by HEV. The optical density at a wavelength of 390 nm is preferably 2.0 or higher because a higher value indicates higher cuttability at that wavelength, and more preferably 2.0 or higher. If the optical density exceeds 5.0, in the case of light absorption, unnecessary high-concentration addition of a light absorbing agent is required, and in the case of light reflection, an excessive number of layers is required, and in the former case, transparency may be reduced or bleed out, and in the latter case, manufacturing costs may be increased or handling may be deteriorated. Therefore, the optical density is preferably 5.0 or lower.

In the laminated film of the present invention, it is preferable that the difference between the maximum value λmax and the minimum value λmin of the cutoff wavelength λ in the wavelength band of 350 nm to 500 nm of the transmission spectrum X with respect to the longitudinal direction of the film, the fluctuation range (λmax-λmin) is 20 nm or less. The cutoff wavelength in the present invention refers to a wavelength that exhibits a half value (an intermediate value between the maximum and minimum transmittances in the wavelength band) in a wavelength band located on the longest wavelength side among wavelength bands in which the transmittance continuously increases by 20% or more in the transmission spectrum X, as shown in FIGS. 7 and 8. In this evaluation as well, the transmission spectrum is evaluated as a spectrum obtained by performing a 10-point average process. In a case where the transmittance continuously monotonically increases as shown in FIG. 7, the wavelength exhibiting the intermediate value between the maximum and minimum transmittance is taken as the cutoff wavelength. In the case of a transmission spectrum having multiple wavelength bands in which the transmittance increases and decreases repeatedly as in Fig. 8 and in which the transmittance continuously increases by 20% or more, the wavelength that represents the median value between the maximum and minimum values in the wavelength band located on the longest wavelength side within the band of 350 nm to 500 nm is set as the cutoff wavelength.

The method for obtaining the laminated film having the above-mentioned spectral shift property will be described in detail later, but for example, a method of strongly stretching in a specific direction and orienting can be exemplified. Specifically, in a biaxial stretching method, a film that is particularly strongly stretched in the long side direction or the width direction of the film can be exemplified. When strongly oriented by stretching in the long side direction or the width direction, the film width may pulsate based on the Poisson's ratio depending on the distance between the rolls in the stretching section between the rolls, resulting in uneven thickness. In addition, in order to strongly stretch in the width direction, the stretching ratio in the long side direction is increased to narrow the film width, resulting in uneven stretching in the stretching process in the long side direction, resulting in uneven thickness after stretching in the width direction. When the laminated configuration is constant, the laminated film thickness and reflection band change in conjunction, so that spectral fluctuations become large due to uneven thickness, which is not preferable for the present laminated film that aims at sharp cutting of a specific wavelength band. Therefore, when measuring the cutoff wavelength in a wavelength band of 350 nm to 500 nm along the long side of the film, by setting the difference between the maximum value λmax and the minimum value λmin of the cutoff wavelength (hereinafter, fluctuation range (λmax-λmin)) to 20 nm or less, it becomes possible to suppress spectral fluctuation, and stably obtain sharp cut property and low-reflection color. When the fluctuation range (λmax-λmin) exceeds 20 nm, there are cases where the reflection color/intensity within the plane of the laminated film significantly changes due to fluctuation in the reflection wavelength band. The fluctuation range (λmax-λmin) is more preferably 15 nm or less, and even more preferably 10 nm or less. An example of a method for controlling the fluctuation range (λmax-λmin) within the above-mentioned range is a method of controlling thickness unevenness according to the stretching conditions described later.

The laminated film of the present invention preferably contains a light absorber in order to improve the cut performance within the reflection wavelength band. The layer containing the light absorber may be an A layer mainly composed of thermoplastic resin A, a B layer mainly composed of thermoplastic resin B, or both the A layer and the B layer. In a method of reflecting light by alternately laminating A layers and B layers like the laminated film of the present invention, it is not easy to completely cut light across the reflection wavelength band because the transmission spectrum changes depending on the combination of two types of thermoplastic resins, the difference in refractive index between thermoplastic resin A and thermoplastic resin B expressed by the stretching process/heat treatment process, the wavelength dependence of the refractive index, and further the layer thickness distribution or film thickness. Therefore, by using light absorption by containing a light absorber and light reflection based on alternate lamination together, sufficient light cut performance can be exhibited more effectively. In addition, when combining light absorption and light reflection, when the wavelength absorbed by the light absorber is designed to partially overlap with the reflected wavelength band, the optical path length increases due to the multiple interference reflection effect derived from the laminated structure, thereby increasing the absorption efficiency and making it possible to easily achieve complete ultraviolet cut compared to the case where the reflection band does not overlap with the band of the light absorber. In addition, since the content of the light absorber can be suppressed compared to the case where light is cut only by light absorption, it has a great advantage from the perspective of suppressing the phenomenon of precipitation on the film surface (bleed out phenomenon).

The light absorber may be contained as an additive within the thermoplastic resin, or may be copolymerized with the thermoplastic resin to more reliably suppress bleed out. When targeting a band of 350 nm to 500 nm in wavelength, examples of the light absorber include ultraviolet absorbers and pigments that absorb HEV, but most of these light absorbers have low molecular weight, and if they are not high molecular weight light absorbers, there are cases where problems such as volatilization in the air when melt-discharged as a sheet, or precipitation on the film surface during a heat treatment process or reliability test, which lead to deterioration of quality, may occur. Therefore, by copolymerizing the light absorber with the thermoplastic resin rather than adding it alone, the ultraviolet absorber can be reliably retained within the layer, and even when contained in the A layer including the thermoplastic resin A located at the outermost layer, it becomes possible to clear the problem of bleed out. In the case of copolymerization with a thermoplastic resin, for example, in the case of copolymerizing a polyester thermoplastic resin and an ultraviolet absorber, this can be achieved by reacting the hydroxyl group terminal contained in most ultraviolet absorbers with the carboxyl group terminal in the polyester resin using an ester exchange reaction or the like.

It is preferable that the light absorber is contained only in the B layer arranged in the inner layer of the laminated film, or that the B layer arranged in the inner layer of the laminated film is contained in greater quantity than the A layer arranged in the outermost layer of the laminated film. In particular, when the laminated film of the present invention is a laminated film in which the A layers are alternately laminated so that they are the outermost layers on both sides, it is most preferable that the light absorber is contained only in the B layer. When contained in the A layer including the outermost layer, since the volume of the amorphous region, which is the region where the additive can remain, is small in the layer using the crystalline resin, the bleed-out phenomenon described above and sublimation/vaporization from the vicinity of the nozzle are likely to occur, contaminating the film forming machine and causing the precipitate to have a negative effect on the processing step. When the ultraviolet absorber is contained only in the B layer, which is the inner layer, the A layer mainly composed of the thermoplastic resin A located in the outermost layer acts as a cover that prevents precipitation of the ultraviolet absorber, so the bleed-out phenomenon is unlikely to occur, which is preferable.

The content of the light absorber is preferably 2.5 wt% or less, more preferably 1.5 wt% or less, and even more preferably 1.0 wt% or less, based on the total weight of the laminated film. If the content is greater than 2.5 wt%, excessive additives are likely to cause bleed out, and may cause whitening of the laminated film, a decrease in light transmittance, and an increase in haze.

In the laminated film of the present invention, the light absorber may be a light absorber that absorbs light in a preferred band, such as an ultraviolet absorber, a visible light absorber, an infrared absorber, etc., but an ultraviolet absorber is preferably used. As the ultraviolet absorber to be used, an organic ultraviolet absorber having a variety of skeletal structures, including a benzotriazole type, a benzophenone type, a benzoate type, a triazine type, a benzoxazine type, and a salicylic acid type, may be used. Among these, an ultraviolet absorber exhibiting heat resistance and low concentration high light absorption is preferably selected from a benzotriazole type and/or a triazine type. In the case of an inorganic ultraviolet absorber, it is not preferable to use it in the laminated film of the present invention because it is incompatible with the thermoplastic resin that serves as the base and causes an increase in haze, thereby worsening the transparency of the laminated film. When two or more types of ultraviolet absorbers are used in combination, ultraviolet absorbers having the same skeletal structure may be used, or ultraviolet absorbers having different skeletal structures may be used. Specific examples are given below. For ultraviolet absorbers existing in a wavelength band with a maximum wavelength of 320 nm or more and 380 nm or less, (※) is added after the compound name.

As the benzotriazole-based ultraviolet absorbent, there are no particular limitations, but examples thereof include 2-(2'-hydroxy-5'-methylphenyl)benzotriazole(※), 2-(2'-hydroxy-3',5'-dite-tert-butylphenyl)benzotriazole(※), 2-(2'-hydroxy-3',5'-dite-tert-butylphenyl)-5-chlorobenzotriazole(※), 2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)benzotriazole(※), 2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole(※), 2-(2'-hydroxy-3',5'-dite-tert-amylphenyl)-5-chlorobenzotriazole(※), 2-(2'-Hydroxy-3'-(3",4",5",6"-tetrahydrophthalimidomethyl)-5'-methylphenyl)-benzotriazole(※), 2-(5-chloro-2H-benzotriazol-2-yl)-6-tert-butyl-4-methylphenol(※), 2,2'-methylenebis(4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazol-2-yl)phenol(※), 2-(2'-hydroxy-3',5'-dite-pentylphenyl)benzotriazole, 2-(2'-hydroxy-5'-tert-octylphenyl)benzotriazole, 2,2'-methylenebis(4-tert-octyl-6-benzotriazolyl)phenol(※), 2-(5-Butyloxy-2H-benzotriazol-2-yl)-6-tert-butyl-4-methylphenol(※), 2-(5-hexyloxy-2H-benzotriazol-2-yl)-6-tert-butyl-4-methylphenol(※), 2-(5-octyloxy-2H-benzotriazol-2-yl)-6-tert-butyl-4-methylphenol(※), 2-(5-dodecyloxy-2H-benzotriazol-2-yl)-6-tert-butyl-4-methylphenol(※), 2-(5-octadecyloxy-2H-benzotriazol-2-yl)-6-tert-butyl-4-methylphenol(※), 2-(5-cyclohexyloxy-2H-benzotriazol-2-yl)-6-tert-butyl-4-methylphenol(※), 2-(5-Propenoxy-2H-benzotriazol-2-yl)-6-tert-butyl-4-methylphenol(※), 2-(5-(4-methylphenyl)oxy-2H-benzotriazol-2-yl)-6-tert-butyl-4-methylphenol(※), 2-(5-benzyloxy-2H-benzotriazol-2-yl)-6-tert-butyl-4-methylphenol(※), 2-(5-hexyloxy-2H-benzotriazol-2-yl)-4,6-dite-tert-butylphenol(※), 2-(5-octyloxy-2H-benzotriazol-2-yl)-4,6-dite-tert-butylphenol(※), 2-(5-dodecyloxy-2H-benzotriazol-2-yl)-4,6-dite-tert-butylphenol(※), Examples include 2-(5-tert-butyloxy-2H-benzotriazol-2-yl)-4,6-di-tert-butylphenol(※).

As triazine-based ultraviolet absorbers, there may be mentioned, but are not particularly limited, 2-(2-hydroxy-4-hexyloxyphenyl)-4,6-diphenyl-s-triazine, 2-(2-hydroxy-4-propoxy-5-methylphenyl)-4,6-bis(2,4-dimethylphenyl)-s-triazine, 2-(2-hydroxy-4-hexyloxyphenyl)-4,6-dibiphenyl-s-triazine, 2,4-diphenyl-6-(2-hydroxy-4-methoxyphenyl)-s-triazine, 2,4-diphenyl-6-(2-hydroxy-4-ethoxyphenyl)-s-triazine, 2,4-diphenyl-6-(2-hydroxy-4-propoxyphenyl)-s-triazine, Examples thereof include 2,4-diphenyl-6-(2-hydroxy-4-butoxyphenyl)-s-triazine, 2,4-bis(2-hydroxy-4-octoxyphenyl)-6-(2,4-dimethylphenyl)-s-triazine, 2,4,6-tris(2-hydroxy-4-hexyloxy-3-methylphenyl)-s-triazine(※), 2,4,6-tris(2-hydroxy-4-octoxyphenyl)-s-triazine(※), 2-(4-isooctyloxycarbonylethoxyphenyl)-4,6-diphenyl-s-triazine(※), 2-(4,6-diphenyl-s-triazin-2-yl)-5-(2-(2-ethylhexanoyloxy)ethoxy)phenol, etc.

It is more preferable that the ultraviolet absorbent used in the present invention have the same basic molecular structure as the above-described ultraviolet absorbent and have the oxygen atom replaced with a sulfur atom of the same group. Specific examples thereof include those in which the ether group of the above-described ultraviolet absorbent is converted into a thioether group, the hydroxyl group into a mercapto group, and the alkoxy group into a thio group. By using an ultraviolet absorbent having a substituent containing a sulfur atom, the thermal decomposition of the ultraviolet absorbent can be suppressed when kneaded into a thermoplastic resin. In addition, by utilizing a sulfur atom and selecting an appropriate alkyl chain, it is possible to suppress the intermolecular force between ultraviolet absorbents and lower the melting point, so that the compatibility with the thermoplastic resin can be improved. By improving the compatibility with the thermoplastic resin, it is possible to maintain high transparency even when the ultraviolet absorbent is added at a relatively high concentration. In particular, it is most preferable to use a sulfur atom-containing benzotriazole-based (hereinafter referred to as thiobenzotriazole) and/or triazine-based ultraviolet absorber (hereinafter referred to as thiotriazine) that has high heat resistance and high absorbency in addition to having good compatibility with polyester resin, which is a preferred thermoplastic resin of the present laminated film.

In the ultraviolet absorbent used in the present invention, it is more preferable that the alkyl chain of the functional group is long. Since the alkyl chain becomes long, the intermolecular interaction is suppressed and it becomes difficult for ring structure packing to occur, so when the laminated film is heat-treated, it becomes difficult for the ultraviolet absorbents to form a crystal structure together, which leads to suppression of whitening of the laminated film after crystallization or bleed out. The length of the alkyl group included in the functional group is preferably 18 or less, more preferably 4 or more and 10 or less, and even more preferably 6 or more and 8 or less. When the length of the alkyl chain is longer than 18, the reaction during the synthesis of the ultraviolet absorbent becomes difficult to proceed due to steric hindrance, which causes a decrease in the yield of the ultraviolet absorbent, which is not realistic.

In the present invention, it is preferable that the light absorber added has a solubility parameter δadd of the light absorber and a solubility parameter δpolym of the thermoplastic resin to which the light absorber is added, which exhibits |δadd-δpolym| ≤ 2.0, so that bleed out is unlikely to occur. Similar to the SP value between the two types of thermoplastic resins constituting the laminated film described above, it is preferable that the solubility parameters of the thermoplastic resin and the light absorber be at the same level, so that the light absorber is easy to disperse when mixed with the thermoplastic resin, and furthermore, bleed out is unlikely to occur due to the absorbers forming different crystal nuclei that are not compatible with the thermoplastic resin. The solubility parameter can be estimated by the calculation method of Hansen or Hoy, but in the present invention, it is estimated based on the estimation method of Fedors, which can be calculated relatively easily. In Fedor's estimation method, it is considered that the cohesive energy density and molar molecular volume of a molecule change depending on the type and number of substituents, and are estimated according to Equation (5). Here, Ecoh (cal/mol) represents cohesive energy, and V represents molar molecular volume (㎤/mol). It is more preferable that the difference in the solubility parameter of the thermoplastic resin to which the light absorber is added and the light absorber is 1.5 or less, and even more preferably 1.0 or less.

The laminated film of the present invention preferably has a transmittance of 20% or less at a wavelength of 390 nm of the transmission spectrum Z at an incident angle of 60°, and a transmittance of 70% or more at a wavelength of 430 nm. When the laminated film of the present invention is mounted and used, light is not only incident from a direction perpendicular to the film surface, and there are cases where sufficient cuttability is required for light from an oblique direction. The reflected wavelength that is interfered and reflected is determined by the difference in refractive index of different thermoplastic resins and the film thickness, but for light that is incident obliquely, the optical path length changes due to the photorefraction phenomenon at the resin interface, so that the reflected wavelength shifts to a shorter wavelength side compared to the case where it is incident vertically. Therefore, even if it is sufficiently cut at vertical incidence, there is a possibility that insufficient cut may occur when light is incident obliquely with respect to the film surface. Therefore, it is preferable to add the above-mentioned ultraviolet absorbent capable of covering the shift in the reflection wavelength band as needed. The transmittance spectrum Z at an incident angle of 60° is preferably such that the transmittance at a wavelength of 390 nm is preferably 15% or less, more preferably 10% or less. In addition, the transmittance at a wavelength of 430 nm is preferably 75% or more.

Below, preferred optical properties other than spectral characteristics of the laminated film of the present invention are described.

The laminated film of the present invention preferably has an in-plane retardation of more than 400 nm and less than 5000 nm. The retardation described in the present invention is a numerical value expressed by the product of the refractive index difference in the direction of orientation in the plane of each thermoplastic resin and the direction perpendicular to the orientation direction, and the film thickness. In the case of a laminated film such as the present invention, it is difficult to individually peel off the layers of the thermoplastic resin and analyze them, so the retardation of the laminated film is determined by an optical measurement method. The retardation can be measured using a commercially available retardation measuring device, such as the KOBRA series manufactured by Oji Geisoku Kiki Co., Ltd., or the WPA-micro manufactured by Photonic Lattice Co., Ltd., or by using the Senarmont method. In the present invention, the retardation is obtained by the measurement method described below using a retardation measuring device (KOBRA-21ADH) manufactured by Oji Geisoku Kiki Co., Ltd. In addition, the measurement wavelength of the retardation is 590 nm unless otherwise specified. In this measurement, the phase difference of the measurement sample and the direction (orientation direction) indicating the maximum refractive index on the film can be measured by tracking the change in transmitted light intensity when the polarizing plates are rotated by sandwiching the sample between two polarizing plates so that the polarization directions are parallel.

The spectral shiftability, which is a feature of the laminated film of the present invention, can be achieved by strongly orienting in a specific direction as described above. Accordingly, since a difference in refractive index occurs in the orientation direction and the direction perpendicular to the orientation direction, the phase difference exhibits a large numerical value compared to the case where the stretching is well-balanced in the longitudinal direction and the width direction. When the in-plane phase difference exhibits within the above numerical range, generally, when combined with a material that transmits only plane polarized light, there are cases where the film appears colored and generates rainbow-colored spots depending on the viewing angle. However, when the laminated film of the present invention is strongly stretched in a specific direction and the orientation axis direction is oriented in a constant direction within the plane, it is possible to significantly suppress the influence of rainbow-colored spots by combining so that the polarizing plane and the orientation direction of the laminated film become parallel. When the in-plane phase difference exhibits 400 nm or less, there are cases where the in-plane refractive index difference is not sufficient due to balanced stretching or low crystallinity of the resin, and the spectral shiftability is weakened. When the in-plane retardation is 5000 nm or more, unless the laminated film thickness is thick, the laminated film is likely to crack in the stretching direction, and it may become difficult to obtain a film sample in a roll state. The in-plane retardation is preferably more than 400 nm and less than 5000 nm, but since the in-plane retardation also depends on the laminated film thickness, it is more preferably more than 400 nm and less than 3000 nm, and most preferably within a range of 500 nm or more and 1500 nm or less.

The in-plane retardation of the laminated film of the present invention is obtained as the average value at three points in total: the center of the film width direction, and the midpoints between the center of the film width direction and both ends in the width direction. Further, it is preferable that the in-plane retardation of the laminated film of the present invention be such that the difference between the maximum and minimum values at three points in total: the center of the film width direction, and the midpoints between the center of the film width direction and both ends in the width direction is 10% or less of the average value of the three points. The film width direction refers to the direction perpendicular to the unwinding direction of the film plane in the case of a roll sample. In the case of a cut sample, the Young's modulus is measured by changing the angle by 5°, and the direction showing the highest Young's modulus is defined as the width direction. Since the in-plane retardation in the film width direction is uniform, even when the laminated film is mounted over a large area, it is preferable because it suppresses the occurrence of multilayer interference unevenness and rainbow-colored spots depending on the position, and also makes the transmission spectrum shift property uniform in the plane. It is preferable that the difference between the maximum and minimum values of the in-plane retardation of the three points be 5% or less of the average in-plane retardation, because this results in a laminated film having a more uniform in-plane retardation in the width direction. In order to make the in-plane retardation in the width direction of the laminated film uniform, it is necessary to make the refractive index state at the width direction position during the stretching process in the width direction uniform. However, in a general biaxially stretched film, due to the effect of the shrinkage force difference caused by the temperature difference in the preheating process or the heat treatment process, an orientation state in the long side direction (bowing phenomenon) in the shape of an arch occurs, so the orientation state (refractive index state) is different at the width direction center position and the width direction end position, and fluctuations occur in the in-plane retardation. Therefore, in order to suppress the shrinkage force in the long side direction during stretching and to make the orientation at the width direction position uniform, it is preferable to provide a temperature gradient in stages in the stretching process. Thereby, the influence of shrinkage based on the Poisson's ratio in the long-side direction that occurs in the widthwise stretching and the influence of the difference in heat shrinkage force caused by the temperature difference in the preheating and heat treatment processes before and after the stretching process can be reduced, and a uniform refractive index difference in the widthwise direction can be expressed in the stretching process. The temperature gradient is preferably performed within a temperature range higher than the glass transition temperature and lower than the crystallization temperature of the laminated film, and further, it is preferable that there be two or more temperature gradients up to the heat treatment temperature.

In addition, it is preferable that the laminated film of the present invention has an orientation angle of 15° or less when the width direction of the film is set to 0° at any of three points: the center of the width direction of the film, and the midpoint between the center of the width direction of the film and both ends in the width direction. The orientation angle at this time is defined as the angle formed by the orientation direction of the film when the width direction (horizontal stretching direction) of the film is used as an angle standard, and is expressed as an absolute value of 0° or more and less than 90°. Specifically, the phase difference measuring device (KOBRA-21ADH) manufactured by Oji Keiki Co., Ltd. described above is used, the film width direction is installed in the device so that the angle is 0° defined by the measuring device, and the numerical value of the orientation angle obtained by measuring is used.

By making the orientation angle in the film width direction 15° or less, the orientation is uniformly distributed over the entire film plane, so that even when the film is laminated at any position in the width direction within the plane, the spectral shift property is preferably provided with a constant effect. In addition, as described below, the present laminated film can be suitably used for a display having a polarizer, but for example, when the transmission/absorption axis of the polarizer and the orientation axis of the present laminated film are laminated so that they are parallel, as is known, it is expected that the occurrence of rainbow color spots due to the birefringence of the laminated film is suppressed, and since the orientation angle is uniform within the plane, the effect can be obtained over a wide range in the width direction, which is preferable. When the orientation angle exceeds 15° in the width direction, the rainbow color spots are strongly confirmed depending on the location where they are viewed, and this is not preferable in applications where the laminated film is mounted and used over a large area because the rainbow color spots worsen the appearance.

In addition, in the present invention, it is preferable that the orientation angle non-uniformity in the film width direction is small. With only the reduction of the shrinkage force in the stretching process described above, the in-plane phase difference can be made uniform even after the stretching process, but due to the shrinkage force caused by the temperature difference before and after the heat treatment process, a state occurs in which the phase difference is uniform but the orientation is different at the center in the width direction and the end in the width direction. Therefore, as a method for reducing the shrinkage force after the stretching process, it is preferable to lower the heat treatment temperature to reduce the shrinkage force on the stretching process side in the long side direction, or to temporarily provide a same-temperature or low-temperature region (a region higher than the glass transition temperature and lower than the stretching temperature of the thermoplastic resin showing the higher temperature among the two types of thermoplastic resins constituting the laminated film) to increase the rigidity of the film. By increasing the rigidity of the film, the influence of shrinkage based on the Poisson's ratio in the long side direction that occurs due to the rebound of stretching in the width direction can be cut off, and the bowing phenomenon can be reduced. In the method of reducing the former heat treatment temperature, there are cases where the crystallization by heat fixation does not progress sufficiently and the heat shrinkage rate increases as a target of the phase difference or orientation angle uniformity. In addition, after suppressing the shrinkage force in the long-side direction, it is preferable to slightly tension the laminated film in the heat treatment process to make it a tensed state. Since shrinkage in the reverse direction (cooling process direction) due to the temperature difference with the cooling process after the heat treatment process is induced and bowing in the stretching process direction that remained before the heat treatment process can be reduced, the orientation in the width direction of the laminated film can be made more uniform.

In the laminated film of the present invention, in the measurement of the heat shrinkage force in the film orientation direction (X direction) and the direction perpendicular to the film orientation direction (Y direction), it is preferable that the rising temperature in both the X direction and the Y direction is 90°C or higher, and further, the shrinkage force at 90°C or higher and 130°C or lower is 250 μN or lower. The heat shrinkage force described here refers to a numerical value obtained using a thermomechanical analyzer (TMA), and is read from the shrinkage force obtained when the temperature is continuously increased from room temperature. The rising temperature of the shrinkage force curve refers to the temperature when the slope of the shrinkage force curve first shows 200 μN/0.1°C. When the rising temperature of the shrinkage force is lower than 90°C, the laminated film is likely to undergo heat shrinkage in the heat treatment process at the time of product mounting and in the long-term heat evaluation after mounting, and there may be cases where the reflection wavelength band changes as the laminated film thickness increases, or the product curls strongly due to the difference in shrinkage force with respect to the bonding material. The rising temperature is also a factor that depends on the type of thermoplastic resin, but is preferably 95°C or higher, more preferably 100°C or higher. In addition, when the shrinkage force at 90°C or higher and 130°C or lower exceeds 250 μN, in a process of bonding a laminated film and another material by roll conveyance, when heat treatment is required, the bonded product may curl due to the difference in shrinkage force during conveyance. The shrinkage force of the laminated film at 90°C or higher and 130°C or lower is more preferably 150 μN or lower, and even more preferably 100 μN or lower.

Below, preferred conditions for the laminated film of the present invention to exhibit high transparency are described.

In the present invention, in a variable-angle photometer, the reflected light intensity in the range of 0°≤θ≤40°, 50°≤θ≤90° is measured, and the horizontal axis is plotted as the angle (°) and the vertical axis as the reflected light intensity, and in a light intensity spectrum obtained, it is preferable that the number of extreme values is 2 or less. A variable-angle photometer continuously changes the angle of a light-receiving portion and detects the light intensity when light emitted from a light source at a specific position is reflected through a sample in an angle-dependent manner. When the sample is a smooth surface, since mainly regular reflected light is detected, the light intensity exhibits a peak at an angle of 45°, and due to the diffusion effect of the emitted light from the light source, the detected light intensity monotonically increases from an incident angle of 0° to 45°, and tends to monotonically decrease when the incident angle exceeds 45° and reaches 90°. However, when there is unevenness on the sample surface, or when there is a segment causing light diffusion inside the sample, reflected light due to diffuse reflection is detected even at an angle other than 45° for regular reflection. Therefore, when diffuse light reflection exists, extreme points due to an increase or decrease in intensity appear in the light intensity spectrum, which would change monotonically. When more than 2 extreme points are detected, it means that the light irradiated on the sample is strongly scattered, and when high transparency is required, such as in the present laminated film, it is particularly preferable that there are fewer extreme points. In the present invention, the extreme value detected in the range of 0°≤θ≤40° and 50°≤θ≤90° is more preferably 1 point or less, and even more preferably 0 point.

The laminated film of the present invention has a multilayer laminated structure and has the special feature of cutting light of a specific wavelength band, and therefore, for example, in construction materials or automobiles, it can be used as a window film, in industrial materials, it can be used as a film for laminating steel plates for signboards, and in laser surface processing, it can be used as a process/release film for photolithography materials, a light-cut film for suppressing adsorption pigment degradation of dye-sensitized solar cells, an optical film for various displays such as smartphones, head-up displays, electronic paper, and digital signage, and in other fields such as food, medicine, and ink, it can be used as a film for the purpose of suppressing photodegradation of contents, etc. In particular, the laminated film of the present invention has the feature of being capable of sharp light cutting while having low reflection and high transparency by irradiating polarized light, and therefore, it can be suitably used for display applications where high transparency is required, polarized sunglasses applications, window films, etc.

Displays utilize various display methods such as liquid crystal display devices, organic EL display devices, quantum dot displays, and micro LED displays, and films exhibiting various functions are arranged inside each display. For example, in the case of a liquid crystal display device, examples include a polarizer protective film or phase difference film constituting a polarizing plate, a surface treatment film bonded to the front surface of the display to add functions, a brightness enhancement film positioned immediately before the backlight, an antireflection film, a transparent conductive base film used for ITO, etc., and an ultraviolet protection film for a touch sensor member. In addition, in the case of an organic EL display device, examples include a λ/4 phase difference film or polarizer protective film constituting a circular polarizing plate arranged on the viewing side (upper side) relative to the light-emitting layer, a surface treatment film bonded to the front surface of the display to provide functions, and various optical films built in for the purpose of protecting the contents from external light. In particular, in order to develop the spectral shiftability of the laminated film of the present invention, the most preferable application location is one in which the spectral shiftability is developed for light emitted from or transmitted inside, and a low-reflective color is exhibited for natural light from the outside reflected on the front surface, and it is most preferable to use it for polarizer protection or screen protection purposes, positioned on the viewing side relative to the polarizing plate of a liquid crystal display or organic EL display using a polarizing plate.

In particular, since the laminated film of the present invention has the characteristics of uniform phase difference and orientation angle within the plane, by arranging it so that the transmission axis direction of the polarizing plate of the display used and the orientation direction of the laminated film or the direction perpendicular to the orientation direction are parallel, it can be suitably used as a screen protection film for a display equipped with an optical fingerprint authentication device. By bonding so as to align the axes, the polarization characteristics of the fingerprint authentication light source transmitted from the polarizing plate are maintained even after transmission through the laminated film, so that the intensity of the fingerprint authentication light source is not impaired, and therefore it can be suitably used. In addition, by designing the phase difference to be an integer multiple of half a wavelength of the fingerprint authentication light source, the fingerprint authentication performance can be further improved.

As a window film, in addition to heat-insulating applications (infrared cut film) for the inner windows of automobiles and buildings, it can also be used to protect polyvinyl butyrate materials used in laminated glass interlayers from ultraviolet rays. In addition, as a light-emitting film, it can also be used to prevent ultraviolet deterioration of particles (such as liquid crystal molecules) that are oriented by voltage application.

Next, a preferred method for manufacturing a laminated film in the laminated film of the present invention is described below. Of course, the present invention is not limited to these examples.

Thermoplastic resin A and thermoplastic resin B are prepared in the form of pellets, etc. The pellets are dried in hot air or under vacuum as needed, and then fed to a separate extruder. Inside the extruder, each thermoplastic resin that has been heated and melted to a melting point or higher is uniformly extruded using a gear pump, etc., and foreign substances and denatured resins are removed through a filter, etc. These thermoplastic resins are formed into a desired shape in a die, and then discharged in the form of a sheet. Then, the sheet discharged from the die is extruded onto a cooling body such as a casting drum, and cooled and solidified to obtain a cast sheet. At this time, it is preferable to use a wire-shaped, tape-shaped, needle-shaped or knife-shaped electrode to contact the cooling body such as the casting drum by electrostatic force and to rapidly cool and solidify. In addition, a method in which air is blown from a slit-shaped, spot-shaped or planar device to contact the cooling body such as the casting drum and to rapidly cool and solidify, or a method in which a nip roll contacts the cooling body and to rapidly cool and solidify, is also preferable.

In addition, a plurality of resins of thermoplastic resin A and thermoplastic resin B are sent from different paths using two or more extruders, and are sent to a multilayer lamination device before being discharged in the form of a sheet. As the multilayer lamination device, a multi-manifold die, a feed block, a static mixer, or the like can be used, but in order to efficiently obtain the multilayer lamination structure of the present invention in particular, it is preferable to use a feed block having fine slits. When such a feed block is used, since the device does not become extremely large, the amount of foreign matter generated due to thermal deterioration is small, and high-precision lamination is possible even when the number of laminations is extremely large. In addition, the lamination accuracy in the width direction is also significantly improved compared to the prior art. In addition, since in this device, the thickness of each layer can be adjusted by the shape (length, width) of the slit, it becomes possible to achieve an arbitrary layer thickness.

The molten multilayer laminated sheet formed in this manner into the desired layer configuration is guided into a die, and a cast sheet is obtained as described above. The obtained cast sheet is then preferably biaxially stretched in the longitudinal direction and the width direction. The stretching may be performed biaxially sequentially or simultaneously. In addition, re-stretching may be performed in the longitudinal direction and/or the width direction.

First, the case of sequential biaxial stretching will be explained. Here, stretching in the longitudinal direction refers to uniaxial stretching for imparting molecular orientation in the longitudinal direction to the sheet, and is usually performed by a difference in the peripheral speed of the rolls, and may be performed in one step, or may be performed in multiple steps using a plurality of roll pairs. The stretching ratio varies depending on the type of thermoplastic resin used, but is usually preferably 2 to 15 times, and when polyethylene terephthalate is used as one of the thermoplastic resins constituting the laminated film, 2 to 7 times is particularly preferably used. In addition, the stretching temperature is preferably set within a range from the glass transition temperature of the thermoplastic resin having a high glass transition temperature among the thermoplastic resins constituting the laminated film to the glass transition temperature + 100°C. When polyethylene terephthalate is used as any of the thermoplastic resins constituting the laminated film, in order to obtain the spectral shift property of the present invention, a stretching ratio in the longitudinal direction of 2.5 to 3.5 times is particularly preferably used. In the case of strong orientation in the stretching process in the longitudinal direction, since neck down occurs in the film width direction, in addition to the inability to obtain a sufficient film width, there are cases where the thickness unevenness or the transmission spectrum unevenness in the longitudinal direction and/or the width direction after stretching in the width direction becomes large.

In this way, the obtained uniaxially stretched laminated sheet is surface-treated as needed by corona treatment, flame treatment, plasma treatment, etc., and then an adhesive layer imparting functions such as easy sliding, easy adhesion, and antistatic properties is applied by inline coating. In the inline coating process, the adhesive layer may be applied to one side of the laminated film, or may be applied to both sides of the laminated film simultaneously or sequentially on one side at a time.

Continuing, the stretching in the width direction means stretching to give a width direction orientation to the sheet, and is usually performed by feeding the sheet while holding both ends of the sheet with clips using a tenter to stretch in the width direction. The stretching ratio varies depending on the type of thermoplastic resin used, but is usually preferably 2 to 15 times, and when polyethylene terephthalate is used as any of the thermoplastic resins constituting the laminated film, 2 to 7 times is particularly preferably used. Furthermore, the stretching temperature is preferably the glass transition temperature of the thermoplastic resin having a high glass transition temperature among the thermoplastic resins constituting the laminated film to the glass transition temperature + 120°C. When polyethylene terephthalate is used as any of the thermoplastic resins constituting the laminated film, in order to obtain the spectrum shift property of the present invention, stretching in the long side direction at the former preferable magnification is applied, and then stretching is preferably applied by 3.5 to 5.5 times in the width direction. By strongly stretching in the width direction, homogeneous spectral shift, phase difference, and orientation can be obtained over a wide range of the film surface.

In this way, the biaxially stretched laminated film is heat treated within a tenter at a temperature higher than the stretching temperature and lower than the melting point, and is uniformly cooled, cooled to room temperature, and then wound up. In addition, when cooling from the heat treatment, relaxation treatment in the long-side direction and/or the width direction may be applied concurrently in order to provide a low orientation angle and thermal dimensional stability of the sheet, if necessary.

In order to achieve both the spectral shiftability and high transparency of the present invention after using polyethylene terephthalate as any of the thermoplastic resins constituting the laminated film, it is preferable that the ratio of the stretching ratio in the width direction and the stretching ratio in the long side direction (a value greater than 1 among the stretching ratio in the width direction/stretch ratio in the long side direction, or the stretching ratio in the long side direction/stretch ratio in the width direction) is 1.1 or more and 3.5 or less. When the stretching ratio is 1.1 or less, the refractive index difference between the alignment direction and the direction perpendicular thereto is not sufficient, so that the spectral shiftability is not expressed and the high transparency may be impaired. When the stretching ratio is greater than 3.5, the spectral shiftability is too strong, so that although high transparency can be achieved, film cracking in one direction is likely to occur, so that the film forming property may be reduced. A more preferable stretching ratio for obtaining a laminated film exhibiting an appropriate spectral shift property and having more preferable durability or low reflection color is 1.4 or more and 2.0 or less.

Next, the case of simultaneous biaxial stretching will be described. In the case of simultaneous biaxial stretching, after surface treatment such as corona treatment, flame treatment, or plasma treatment is performed on the obtained cast sheet as needed, functions such as easy sliding, easy adhesion, and antistatic properties may be imparted through inline coating. In the inline coating process, the easy adhesion layer may be applied to one side of the laminated film, or may be applied to both sides of the laminated film simultaneously or sequentially on one side at a time.

Next, the cast sheet is guided to a simultaneous two-axis tenter, and while holding both ends of the sheet with clips, it is returned to be stretched in the long side direction and the width direction simultaneously and/or stepwise. As the simultaneous two-axis stretching machine, there are a pantograph type, a screw type, a drive motor type, and a linear motor type, but a drive motor type or a linear motor type that can arbitrarily change the stretching ratio and can perform relaxation processing at any location is preferable. The stretching ratio varies depending on the type of resin, but usually, an area magnification of 6 to 50 times is preferable, and when polyethylene terephthalate is used as any of the thermoplastic resins constituting the laminated film, an area magnification of 8 to 30 times is particularly preferable. In order to strongly express orientation in a specific direction within the plane, it is preferable that the stretching ratios in the long side direction and the width direction be different values. The stretching speed may be the same speed, or stretching in the long side direction and the width direction may be performed at different speeds. In addition, as the stretching temperature, a temperature range of the glass transition temperature to the glass transition temperature + 120°C of the thermoplastic resin that exhibits a high temperature among the thermoplastic resins constituting the laminated film is preferable.

In order to provide the sheet thus simultaneously stretched in two axes with flatness and dimensional stability, it is preferable to subsequently perform a heat treatment within the tenter at a temperature higher than the stretching temperature and lower than the melting point. During this heat treatment, in order to suppress the distribution of the main orientation axes in the width direction, it is preferable to momentarily perform a relaxation treatment in the longitudinal direction immediately before and/or immediately after entering the heat treatment zone. After the heat treatment in this manner, it is uniformly annealed, cooled to room temperature, and then wound up. Furthermore, if necessary, a relaxation treatment may be performed in the longitudinal direction and/or the width direction when annealing from the heat treatment. The relaxation treatment is momentarily performed in the longitudinal direction immediately before and/or immediately after entering the heat treatment zone.

The laminated film obtained as described above is trimmed to a required width through a winding device and wound in a roll state so that no winding wrinkles are formed. In addition, embossing may be performed on both ends of the sheet during winding to improve the winding shape.

The thickness of the laminated film of the present invention is not particularly limited, but is preferably 5 ㎛ or more and 100 ㎛ or less. Considering the thin film tendency of various functional films and the high-end characteristic of flexibility, it is preferably 40 ㎛ or less, and more preferably 25 ㎛ or less. Although there is no lower limit, in order to provide sufficient light cut property without bleed out while simultaneously utilizing the addition of a light absorber and light reflection by the laminated structure, it is necessary to have a certain thickness. In addition, in order to make the roll winding property stable and to form the film without rupture, it is realistically preferable to have a thickness of 10 ㎛ or more.

It is preferable that the inline coating layer that can be applied to the outermost surface of the laminated film of the present invention has antistatic properties. In the process of conveying a roll of the laminated film, there are cases where the laminated film becomes charged due to friction between the roll and the laminated film, causing attachment of dust or the like, thereby causing a problem in which the rollability deteriorates due to warping or wrinkles in the laminated film. The antistatic properties can be expressed by a surface resistance value, and it is preferable that it exhibits a numerical value of 1.0×10 ⁷ Ω/□ or more and 1.0×10 ¹³ Ω/□ or less in an environment of 23°C and 65%RH, and more preferably a numerical value of 1.0×10 ⁸ Ω/□ or more and 1.0×10 ¹⁰ Ω/□ or less. When the resistance value is smaller than 1.0×10 ⁷ Ω/□, there are cases where malfunction due to electrical interaction occurs in display applications in which it can be suitably used. In the case of a resistance value greater than 1.0×10 ¹³ Ω/□, since it indicates an electrically insulating state, there are cases where the generation of static electricity cannot be suppressed due to poor anti-static properties.

The antistatic agent is not particularly limited, but compounds having a phosphate group, a sulfonate group, an alkali sulfonate, or an ionized nitrogen atom can be used. It is preferable that the antistatic agent be contained in a weight ratio of 10% or more and 50% or less with respect to the total weight of the coating solids.

In addition, a hard coat layer composed mainly of a curable resin may be laminated on the uppermost surface of the laminated film of the present invention in order to add functions such as scratch resistance, dimensional stability, and adhesiveness/adhesion. When the laminated film is returned roll-to-roll for mounting on a product, the occurrence of scratches on the surface of the laminated film due to friction between the roll and the laminated film can be prevented. In addition, even in cases where the resin oligomer component in the laminated film or various additives that can be added to the laminated film are likely to bleed out during high-temperature heat treatment, by providing a hard coat layer on the uppermost surface, a hard coat layer having a high crosslinking density can exhibit a precipitation-suppressing effect. In addition, by laminating a curable resin layer, it is possible to suppress dimensional changes in the film due to heat treatment, and it is possible to suppress increases in film thickness due to heat shrinkage and changes in optical properties such as the transmittance spectrum of the laminated film that accompany this.

Since the hard coat layer has superior characteristics in the present laminated film, it is preferable to apply it to at least one side of the laminated film in order to maintain the properties of the film, particularly the film dimensions. The hard coat layer can also be applied to both sides of the laminated film, but since there is a possibility that the slipperiness of the film and further the windability of the roll may deteriorate due to the hard coat layers adhering to each other, it is preferable to apply the hard coat layer to only one side, or when applying it to both sides, to perform a surface roughening treatment such as particle addition or atmospheric plasma or vacuum plasma on at least one side to impart slipperiness.

The hard coat layer may be laminated directly on the uppermost surface of the laminated film, but it is more preferable to laminate it via an inline coating layer. When the difference in refractive index between the hard coat layer and the thermoplastic resin on the uppermost surface of the laminated film is large, this is preferable because the adhesion between the two can be improved by adjusting the refractive index of the inline coating layer. The refractive index of the inline coating layer is preferably a value between the refractive index of the thermoplastic resin A or the thermoplastic resin B constituting the laminated film and the refractive index of the curable resin C constituting the hard coat layer, and more preferably a value intermediate between the refractive indices of the two resins (when the refractive index of the thermoplastic resin A or the thermoplastic resin B is α and the refractive index of the curable resin C constituting the hard coat layer is β, it is 0.98 x (α + β) / 2 or more and 1.02 x (α + β) / 2 or less). For example, when using polyethylene terephthalate as a thermoplastic resin located on the uppermost surface of a laminated film and an acrylic resin as a curable resin, the former has a refractive index of about 1.65 after stretching, and the latter has a refractive index of about 1.50, so that the difference in refractive indices is large, which may possibly cause poor adhesion. Therefore, it is preferable that the refractive index of the inline coating layer has a value of 1.50 or more and 1.60 or less, and more preferably, it is a refractive index of 1.55 or more and 1.58 or less.

As a curable resin that can be used in the hard coat layer, one that is highly transparent and durable is preferable, and for example, acrylic resin, urethane resin, fluorine-based resin, silicone resin, polycarbonate-based resin, and vinyl chloride-based resin can be used alone or in combination. In terms of curability, flexibility, and productivity, it is preferable that the curable resin includes an active energy ray-curable resin such as an acrylic resin represented by a polyacrylate resin. In addition, when adding scratch resistance, it is preferable that the curable resin includes a thermosetting urethane resin.

The active energy ray in the present invention refers to various electromagnetic waves such as ultraviolet rays, electron rays, and radiation (α rays, β rays, γ rays, etc.) that polymerize vinyl groups of acrylics. Ultraviolet rays are the simplest and therefore preferable in practical terms. As an ultraviolet source, an ultraviolet fluorescent lamp, a low-pressure mercury lamp, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a xenon lamp, a carbon arc lamp, etc. can be used. In the case of curing by an ultraviolet source, it is preferable that the oxygen concentration be as low as possible in order to prevent oxygen inhibition, and it is more preferable to cure in a nitrogen atmosphere or an inert gas atmosphere. In addition, in the case of the electron beam method, the device is expensive and operation under an inert gas is required, but it is advantageous in that it is not necessary to contain a photopolymerization initiator or a photosensitizer.

Hereinafter, the present invention will be described by way of examples, but the present invention is not limited to these examples. Each characteristic was measured by the following method.

(Method of measuring characteristics and method of evaluating effects)

The method for measuring characteristics and evaluating effects in the present invention are as follows.

(1) Layer thickness, number of layers, and layer structure

The layer composition of the laminated film was determined by transmission electron microscopy (TEM) observation of a sample whose cross-section was cut using a microtome. That is, a transmission electron microscope H-7100FA (manufactured by Hitachi, Ltd.) was used to observe the cross-section of the laminated film under conditions of an acceleration voltage of 75 kV, take a cross-sectional photograph, and measure the layer composition and the thickness of each layer. In addition, in some cases, a dyeing technique using RuO ₄ or OsO ₄ was used to obtain high contrast. In addition, among all the layers introduced into a single image, observation was performed at a magnification of 100,000 times when the thin film layer thickness was less than 50 nm, 40,000 times when the thin film layer thickness was 50 nm or more but less than 500 nm, and 10,000 times when it was 500 nm or more, to specify the layer thickness, number of laminates, and laminated structure.

(2) Measurement of transmittance and transmission spectrum

A sample was cut into a square with one side measuring 4 cm from the center of the width direction of the laminated film, and a phase difference measuring device (KOBRA-21ADH) manufactured by Oji Geisoku Kiki Co., Ltd. was used to install the sample in the device so that the film width direction was at an angle of 0° defined by this measuring device, and the alignment angle when irradiated with a wavelength of 590 nm at an incident angle of 0° was measured and read. When the measurement result could not be obtained because light with a wavelength of 590 nm was reflected by the laminated film, the alignment angle was measured by appropriately selecting a wavelength that was not reflected among wavelengths 480 nm, 550 nm, 630 nm, and 750 nm. The direction indicated by the obtained alignment angle was defined as the X direction, and the direction perpendicular thereto was defined as the Y direction. Next, the transmission spectrum was measured using a spectrophotometer U-4100 manufactured by Hitachi High-Tech Sciences. A Glenn-Taylor polarizing prism (MGTYB20) and an integrating sphere manufactured by Karl Lamprecht Co., Ltd. were installed in the device, and the transmission direction of the Glenn-Taylor polarizing prism, the orientation direction of the sample (X direction) and the direction perpendicular to the orientation direction (Y direction) were aligned, and a graph of the variation in light transmittance in a wavelength range of 295 nm to 905 nm was measured when the reflection of an aluminum oxide standard white plate (included with the main body) was set to 100%. Measurements were continuously made under these measurement conditions, with the scan speed set to 600 nm/min and the sampling pitch set to 1 nm.

(3) 10-point average processing of the transmission spectrum

For the 1 nm pitch transmittance spectrum data obtained in the transmittance measurement of the above (2), the average value of the transmittance data of 10 points before and after was calculated (for example, when data from 295 nm to 304 nm were used, the average transmittance data of 299.5 nm was calculated. After that, data at 1 nm pitch from 299.5 nm to 900.5 nm was calculated by performing the process up to 905 nm). After that, the average value of two adjacent points was calculated in order (for example, the average transmittance data of 300 nm was calculated from the average of 299.5 nm and 300.5 nm), and by repeating the same calculation, the average transmittance data of 10 points with a wavelength of 300 nm to 900 nm was obtained.

(4) Optical density at wavelength 390 nm

In the 10-point average-processed transmittance data (transmittance spectrum X) obtained from the transmittance measurement of (2) above, the transmittance at a wavelength of 390 nm was read, and the transmittance was converted from % notation to decimal notation, and then substituted into equation (4) to calculate the optical density.

(5) Fluctuation range (λmax-λmin)

In the central portion of the laminated film in the width direction, a strip sample with a film width of 5 cm and a film long side direction of 3 m was cut out. For the central position of the film width of 5 cm, a transmission spectrum was obtained by averaging 10 points in a wavelength range of 300 nm to 800 nm in the same manner as in (2) using a spectrophotometer U-4100 manufactured by Hitachi High-Tech Sciences. This operation was repeated at 10 cm intervals in the long side direction, and a total of 30 points of transmission spectrum data were obtained. After performing 10-point averaging on the transmission spectrum of each point, the cutoff wavelength λ of each spectrum data was read. Among the 30 cutoff wavelengths λ, the maximum wavelength was designated as λmax, and the minimum wavelength was designated as λmin, and the fluctuation range (λmax-λmin) was calculated.

(6) Young's rate

The film was cut into a rectangular shape measuring 15 cm in length and 1.5 cm in width, and used as a sample for measuring Young's modulus. In the measurement according to JIS-K7127-1999, Robot Tensilon RTA (Orientec) was used to measure at a temperature of 23°C and a humidity of 65%RH. In addition, the tensile speed was 300 mm/min. The measurement was performed at angles of 5° with respect to the cut sample, and the direction with the highest Young's modulus was the film width direction.

(7) Phase difference/orientation angle within the plane

A phase difference measuring device (KOBRA-21ADH) manufactured by Oji Geisoku Kiki Co., Ltd. was used. A sample was cut into 4 cm in the width direction × 4 cm in the long side direction from three locations: the center of the width direction of the laminated film, and the midpoint between the center and both ends in the width direction. The sample was installed in the device so that the film width direction became an angle of 0° defined by the measuring device, and the in-plane phase difference and the orientation angle at a wavelength of 590 nm at an incident angle of 0° were measured and read. In cases where the measurement result could not be obtained because light at a wavelength of 590 nm was reflected by the laminated film, a wavelength that was not reflected was appropriately selected from among wavelengths of 480 nm, 550 nm, 630 nm, and 750 nm for measurement, and the phase difference at a wavelength of 590 nm was calculated using Cauchy's dispersion formula.

(8) Variophotometer

A goniophotometer (GP-200) manufactured by Murakami Shikisai Gijutsu Kenkyujo was used. The optical aperture was set to 1, the light receiving aperture was set to 3, and when the sample was placed at 45° to the optical path, the light receiving section was angled from 0° to 90° to track the transmitted light quantity, and the number of extreme values when the horizontal axis was plotted as the angle (°) and the vertical axis as the transmitted light quantity was evaluated.

(9) Measurement of heat shrinkage

A thermomechanical measuring device (TMA/SS6000) manufactured by Seiko Instruments was used. A sample having a width of 4 mm and a length of 70 mm was cut out from the center in the width direction in each of the direction perpendicular to the film orientation direction and the direction in the direction perpendicular to the film orientation direction. The sample was fixed to one end of a clip with a chuck distance of 20 mm, and a load of 3 g was applied, thereby fixing the clip at the other end, thereby fixing the sample between the clips of the device. The temperature was increased from 25°C (room temperature) to 160°C at a heating rate of 10°C/min, and the shrinkage force of the sample in a constant length state was tracked, and the rising temperature (°C) and the shrinkage force (μN) at 90°C or more and 130°C or less were evaluated.

(10) Surface resistance measurement

An Advantest digital ultra-high resistance/micro-current electrometer R8340 was used. Three square samples each measuring 10 cm from the center in the width direction were cut out to serve as test pieces. After regulating humidity for 24 hours under conditions of 23°C and 65% RH, the test pieces were set in a resistivity chamber (12702A), and the press-fit sample was pressed against the electrode to the position of memory 3 to measure the surface resistance. This operation was performed for three test piece samples, and the average value was used as the measured value.

(11) DSC measurement

A differential scanning calorimeter EXSTAR DSC6220 manufactured by Seiko Denshi Kogyo Co., Ltd. was used. Measurements and temperature readings were performed in accordance with JIS-K-7122 (1987). 10 mg of a sample was heated from 25°C to 300°C at a rate of 10°C/min on an aluminum tray, then rapidly cooled, and then heated again from 25°C to 300°C at a rate of 10°C/min. The temperature at the intersection of the baseline when the temperature was increased from room temperature and the tangent line at the inflection point of the step transition portion was taken as the glass transition temperature, and the peak top of the exothermic peak was taken as the crystallization temperature.

(12) Lamination of hard coat layer

A laminated film having an adhesive-friendly layer applied thereto was used as a base material, and application was performed using a continuous application device having a die coater. As a resin constituting the hard coat layer, an ultraviolet-curable urethane acrylic resin, JAGO UV-1700B [refractive index: 1.50 to 1.51] manufactured by Nippon Gosei Kagaku Kogyo Co., Ltd., was used. The die coat device consists of an application process, drying processes 1 to 3, and a curing process. In the application process, the laminated film was continuously conveyed at a set conveyance speed, and continuous application was performed at a constant coating thickness through the die coat device. Application was performed by adjusting the conveyance speed so that the coating thickness of the hard coat layer (solid content thickness after drying) was 3 μm. The drying process is equipped with three rooms in total, and has a nozzle capable of blowing hot air parallel to the conveyance direction of the laminated film, and a far-infrared heater. In each drying process, the temperature and the wind speed (fan rotation speed) of the hot air can be set independently, and these are the same on the hard coat lamination side of the laminated film and its back side. The temperature of each drying process was 80℃. The actual temperature of the hot air was measured using the value from the sensor attached to the die coating device. The curing process was performed following drying processes 1 to 3, and was performed under the conditions of a UV irradiation device, a nitrogen atmosphere (oxygen concentration 0.1 vol% or less), an accumulated light amount of 200 mJ/cm2, and an irradiation light intensity of 160 W/cm.

(13) Bleed Out (Haze Evaluation)

The laminated film thus prepared was cut into pieces measuring 10 cm in the long side x 10 cm in the width direction from the center of the width direction of the film, sandwiched between sheets of plain paper, and left in an 85°C, airless oven for 500 hours, and the change in haze value of the laminated film before and after heat treatment was evaluated. The haze was measured using a haze meter (HGM-2DP) manufactured by Suga Test Instruments Co., Ltd. in accordance with the old JIS-K-7105 (1981 edition). Five arbitrary points within the laminated film surface were measured, and the average value was used as the measurement result.

S: Haze value fluctuation is less than 0.5%

A: Haze value fluctuation is 0.5% or more and less than 1.0%

B: Haze value fluctuation is 1.0% or more and less than 1.5%

C: Haze value fluctuation is 1.5% or more

(14) Field evaluation

(14-1) Mounting of laminated films

The iPhone 6, a smartphone manufactured by Apple Inc., was used. The liquid crystal panel was separated, and a laminated film was attached to the most visible surface of the polarizing plate, which was located on the most visible side, using an optical adhesive (OCA) so that the transmission axis direction of the polarizing plate and the orientation direction of the laminated film were aligned. The polarizing plate with the laminated film mounted thereon was then built into the housing of the iPhone 6 and used as a test piece for accelerated weathering tests.

(14-2) Color evaluation before and after installation

The reflection colorimetric value in the black display of the screen was measured using a spectrophotometer CM3600d manufactured by Konica Minolta Sensing Co., Ltd. The change in the reflection color before and after incorporating the laminated film of the present invention into the display was evaluated. The measurement conditions were a measurement diameter of 8 mm, a viewing angle of 10°, and a light source of D65, and the a* value and b* value in the reflection SCI were read. The superiority of the color change was evaluated according to the amount of change in the color value according to equation (6).

Equation (6) Color change = √{(a* after test - a* before test) ² + (b* after test - b* before test) ² }

S: Color change before and after acceleration test is less than 2

A: The color change before and after the acceleration test is 2 or more and less than 5.

B: Color change before and after the accelerated weathering test is 5 or more and less than 10

C: Color change before and after the accelerated weathering test is 10 or more

(15) Accelerated weather test

(15-1) Accelerated weather test

A display mounted with a laminated film was installed in a Sunshine Weathermeter SS80 manufactured by Suga Test Equipment Co., Ltd. with the viewing side facing the light irradiation surface, and an accelerated weather test of 500 hours was performed. The device has a spectrum three times as strong as sunlight, and can perform tests that simulate long-term outdoor use. The treatment conditions were as follows: a temperature inside the tank of 60°C, a humidity inside the tank of 50%RH, an illuminance of 180 W/㎡, and no shower treatment.

(15-2) Display mounting and contrast (brightness) evaluation

The measurement was performed using a BM7 luminance measuring device manufactured by Topcon Technohouse. The luminance in the full-surface white display was A, and the luminance in the full-surface black display was B, and the contrast value was calculated according to Equation (7). The superiority was evaluated as follows based on the amount of change in contrast before and after the accelerated weathering test.

Equation (7) Contrast = B/A

S: Contrast change before and after the acceleration test is less than 3%

A: The change in contrast before and after the acceleration test is 3% or more and less than 5%.

B: The change in contrast before and after the acceleration test is 5% or more and less than 10%.

C: Contrast change before and after the acceleration test is 10% or more

(15-3) Display placement and color evaluation

The reflection colorimetric values in the black display of the screen were measured using a spectrophotometer CM3600d manufactured by Konica Minolta Sensing Co., Ltd. The change in the reflection color before and after the accelerated weather test was evaluated. The measurement conditions were a measurement diameter of 8 mm, a viewing angle of 10°, and a light source of D65, and the a* and b* values in the reflection SCI were read. The superiority of the color change was evaluated according to the amount of change in the color value according to the above formula (6).

S: Color change before and after acceleration test is less than 2

A: The color change before and after the acceleration test is 2 or more and less than 5.

B: Color change before and after the accelerated weathering test is 5 or more and less than 10

C: Color change before and after the accelerated weathering test is 10 or more

Example

(Example 1)

As thermoplastic resin A, polyethylene terephthalate (PET) resin having a refractive index of 1.58 and a melting point of 255°C was used. In addition, as thermoplastic resin B, polyethylene terephthalate (PET/CHDM30) copolymerized with cyclohexanedimethanol (CHDM), a microcrystalline resin having a refractive index of 1.57, at 30 mol% with respect to the diol component was used. The prepared thermoplastic resin A and thermoplastic resin B (copolymer resin) were each fed into two twin-screw extruders in pellet form, and both were melted at 280°C and kneaded. The kneading conditions were such that the discharge amount per screw rotational speed was 0.7. Next, after interposing seven FSS type leaf disc filters, they were joined to a feed block having 501 slits while metering with a gear pump to form an alternate laminate in which 501 layers were alternately laminated in the thickness direction at a lamination ratio of 1.0. Here, the slit length was designed to be step-like, and the slit spacing was all constant. The obtained alternating laminated film was configured such that the final laminated film had two thermoplastic resin A layers in contact with the outermost surface each had a thickness of 3 µm, and the thickness of the other internal layers was in the range of 50 nm to 80 nm, and furthermore, the A layers mainly composed of thermoplastic resin A had a total of 251 layers, and the B layers mainly composed of thermoplastic resin B had a total of 250 layers, and that they were alternately laminated in the thickness direction, as confirmed by observation with a transmission electron microscope. In addition, the layer thickness had a two-stage slope configuration in which the thickness monotonically increased from one end to the center, and monotonically decreased from the center to the other end. The alternating laminated product was supplied to a T die and formed into a sheet, and then, while applying an electrostatic voltage of 8 kV with a wire, it was rapidly cooled and solidified on a casting drum whose surface temperature was maintained at 25°C to obtain an unstretched laminated cast sheet.

After the obtained laminated cast sheet was heated in a roll group set to 90°C, it was rapidly heated from both sides of the film by a radiation heater between stretching sections of 100 mm, and stretched 3.0 times in the long direction of the film, and then once cooled. Subsequently, corona discharge treatment was performed in the air on both sides of this laminated uniaxially stretched film, the wetting tension of the base film was set to 55 mN/m, and #4 meta bar was used on both sides of the film to coat an aqueous coating agent containing a vinyl acetate-acrylic resin containing 3 wt% of colloidal silica having a particle size of 100 nm to serve as an easy-slip layer (hereinafter, performing coating means the above content), thereby forming an easy-adhesive layer. This uniaxially laminated film was guided to a tenter, preheated with hot air at 90°C, and then stretched 3.5 times in the film width direction at a temperature of 140°C. The stretched film was heat-treated with hot air at 230°C in a tenter immediately after stretching was completed, and then relaxed 1% in the width direction under the same temperature conditions, and then wound up to obtain a laminated film. The laminated film had a thickness of 35 μm, and TEM observation showed that the thickness of the adhesive-friendly layer was about 60 nm on both sides. In addition, when the transmission spectrum was measured with a spectrophotometer, it was found to have long-wavelength ultraviolet ray cutability that increased in the range of a wavelength of 370 to 410 nm. The basic performance including the phase difference is as shown in Table 1, and the variation in the haze value in the bleed-out property evaluation was 0.6%, which was a good result.

In the evaluation when mounted on a display, it was confirmed that although the cutability in the ultraviolet range was slightly lacking because the ultraviolet and long-wavelength ultraviolet ranges were cut only by light reflection, it had sufficient performance for mounting and use.

(Example 2)

In Example 1, as the thermoplastic resin B, polyethylene terephthalate (PET/SPG15/CHDC20), in which cyclohexanedicarboxylic acid (CHDC), which is an amorphous resin having a refractive index of 1.55 and does not have a melting point, is copolymerized with 20 mol% of the dicarboxylic acid component and 15 mol% of spiroglycol (SPG) as the diol component, was used, and the extrusion temperature of the thermoplastic resin B was set to 260°C, was obtained in the same manner as in Example 1, except that a laminated film was obtained. Compared with Example 1, since the refractive index difference increased, the reflectivity increased, and the maximum region area exhibiting spectral shift properties increased. Because of the amorphous resin, the in-plane phase difference also decreased, and the orientation angle in the width direction decreased slightly, although not sufficiently. In the mounting evaluation, since the ultraviolet ray cutoff property increased, the contrast decrease in the brightness evaluation was suppressed compared with Example 1 (Table 1).

(Example 3)

In Example 2, a laminated film was obtained in the same manner as in Example 2, except that the total thickness of the laminated film was 72 μm and a benzotriazole-based ultraviolet absorber (2,2'-methylenebis(4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazol-2-yl)phenol)) was added in an amount of 3 wt% with respect to the resin composition constituting the B layer including thermoplastic resin B as a main component. By targeting the boundary between the red visible light and near-infrared regions, a laminated film that was highly transparent and capable of effectively cutting high-energy near-infrared rays could be obtained (Table 1).

(Comparative Example 1)

In Example 1, both thermoplastic resin A and thermoplastic resin B were made of polyethylene terephthalate (PET) resin having a refractive index of 1.58 and a melting point of 258°C, to obtain a film having a single film configuration. It had no ultraviolet ray cut properties at all, and since it was a single film configuration, deterioration was remarkable in the bleed-out properties and accelerated weather resistance test after mounting (Table 5).

(Example 4)

In Example 2, a laminated film was obtained in the same manner as in Example 2, except that a benzotriazole-based ultraviolet absorber (2,2'-methylenebis(4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazol-2-yl)phenol)) was added to the thermoplastic resin B so as to be 2 wt% with respect to the resin composition constituting the B layer having the thermoplastic resin B as the main component. The ultraviolet range cut could be made sufficient by the combined use of light absorption and light reflection. On the other hand, since an ultraviolet absorber having low compatibility with the resin was used, the bleed-out property was worse than in Example 2 (Table 1).

(Comparative Example 2)

A film was obtained in the same manner as in Comparative Example 1, except that a polyethylene terephthalate resin was used, to which a benzotriazole-based ultraviolet absorber (2,2'-methylenebis(4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazol-2-yl)phenol)) was added in an amount of 4 wt% with respect to the resin composition, as thermoplastic resin A and thermoplastic resin B. Since a single-film film with general ultraviolet absorber addition cannot obtain long-wavelength cut property due to light reflection, it is necessary to add the ultraviolet absorber at a high concentration, and the bleed-out property was significantly poor, so that it did not have a performance capable of withstanding long-term use (Table 5).

(Comparative Example 3)

A film was obtained in the same manner as in Comparative Example 1, except that a polyethylene terephthalate resin was used, to which a thiobenzotriazole-based ultraviolet absorber (2-(5-dodecylthio-2H-benzotriazol-2-yl)-6-tert-butyl-4-methylphenol) was added as thermoplastic resin A and thermoplastic resin B in an amount of 1.5 wt% with respect to the resin composition. Although the long-wavelength ultraviolet cut property was satisfied by using an ultraviolet absorber having long-wavelength ultraviolet cut property, the cut property in the ultraviolet range was not satisfied, and deterioration occurred after the durability test (Table 5).

(Comparative Example 4)

A film was obtained in the same manner as in Comparative Example 1, except that the same thiobenzotriazole-based UV absorber as that used in Comparative Example 3 was added as an UV absorber so as to be 3 wt% with respect to the resin composition. Although it was added at a high concentration to satisfy the UV range, the bleed-out property was slightly insufficient, and since the light absorber could not sharply cut the long-wavelength UV range, the entire film had a yellow color, and it became a laminated film with remarkable coloring in screen display (Table 5).

(Comparative Example 5)

In Example 4, a laminated film was obtained in the same manner as in Example 4, except that the stretching ratio in the longitudinal direction was 3.3 times, the stretching ratio in the width direction was 3.5 times, and the cast drum speed was reduced in accordance with the stretching ratio to make the laminated film thickness 35 µm. Since the difference in stretching intensity in two mutually perpendicular directions was small, almost no spectral shift occurred. Although the shape of the average transmission spectrum Z was the same as in Example 4, it was a laminated film in which visible light was reflected on the front surface and coloring in image display was enhanced (Table 5).

(Comparative Example 6)

In Example 4, a laminated film was obtained in the same manner as in Example 4, except that the cast drum speed was increased and the laminated film thickness was set to 34 μm. Since the reflection band was covered by the shadow of the absorption curve derived from the added ultraviolet absorbent, the spectral shiftability was hardly expressed. Since the cutability from the ultraviolet region to the HEV region was insufficient, the laminated film did not have durability (Table 5).

(Example 5)

In Example 4, a laminated film was obtained by joining feed blocks having 51 slits and alternately laminating 49 layers in the thickness direction with a lamination ratio of 1.0. Further, the uniaxially stretched laminated film was guided into a tenter and stretched 5.0 times in the film width direction at a temperature of 140°C. A laminated film was obtained in the same manner as in Example 4, except that the two outermost layers each had a thickness of 3 μm, the 49 middle layers had a thickness of 50 nm or more and 70 nm or less, and the laminated film had a single-stage slope configuration in which the layer thickness monotonically increased from one end to the other, and the film thickness was 10 μm. The number of laminates was small, and it had sufficient minimum performance for use from the viewpoints of light reflectivity and bleed-out properties (Table 1).

(Example 6)

In Example 4, a feed block having 201 slits was joined to obtain a laminated film in which 201 layers were alternately laminated in the thickness direction with a lamination ratio of 1.0. Furthermore, a laminated film was obtained in the same manner as in Example 4, except that the uniaxially stretched laminated film was guided to a tenter and stretched 4.5 times in the film width direction at a temperature of 140°C. The obtained laminated film had two outermost layers each having a thickness of 100 nm, 199 middle layers having a thickness of 60 to 80 nm, a layer thickness of a one-step inclined configuration, and a film thickness of 14 μm. By using the one-step inclined configuration, the cutness of transmitted light became sharper than in Example 4.

(Example 7)

In Example 4, two different types of thermoplastic resins were joined to a feed block having 801 slits, and a laminated film was formed by alternately laminating 801 layers in the thickness direction with a lamination ratio of 1.0. A laminated film was obtained in the same manner as Example 4, except that the two outermost layers had a thickness of 3 µm each, the 799 middle layers had a thickness of 50 to 80 nm, and the layer thickness was 55 µm. The layer thickness had a three-stage inclination structure in which it monotonically increased from one end to the 1/3 position of the layer thickness, monotonically decreased from the 1/3 position to the 2/3 position, and further monotonically increased from the 2/3 position to the other end. Since the number of layers is large and the three-stage inclination structure is high, the bleed-out properties and durability during long-term use are excellent in that the reflectivity is high, but the color tone change before and after mounting was at the same level as Example 4 (Table 2).

(Example 8)

In Example 4, a laminated film was obtained in the same manner as in Example 4, except that the uniaxially stretched laminated film was guided into a tenter and stretched 5.0 times in the film width direction at a temperature of 140°C. As a result of the improvement in spectral shift properties, the coloration after mounting was reduced (Table 2).

(Example 9)

In Example 4, a laminated film was obtained in the same manner as in Example 4, except that the uniaxially stretched laminated film was guided into a tenter, stretched 6.0 times in the film width direction at a temperature of 140°C, and the cast drum speed was adjusted to a thickness of 34.5 μm. A laminated film was obtained that strongly shielded blue light under polarization conditions (X-wave irradiation conditions) while suppressing blue reflection overall, and had properties based on the concept of spectrum shiftability (Table 2).

(Example 10)

In Example 4, a laminated film was obtained in the same manner as in Example 4, except that stretching was not performed in the longitudinal direction, stretching was performed 3.0 times in the film width direction at a temperature of 140°C, and the cast drum speed was increased so that the thickness became 35 μm in accordance with the stretching ratio. Since stretching was performed in a uniaxial direction, only the reflective cut property in the orientation direction was strongly expressed, and it was a laminated film suitable for the concept of low reflection color, high transparency, and sharp cut property (Table 2).

(Comparative Example 7)

In Example 4, a laminated film was obtained in the same manner as in Example 4, except that stretching in the longitudinal direction was not performed, stretching was performed 5.0 times in the film width direction at a temperature of 140°C, and the cast drum speed was increased so that the thickness became 35 μm in accordance with the stretching ratio. The film was difficult to form continuously because cracking in the width direction was remarkable. Since the spectral shift property was too strong, reflection color spots and rainbow-colored spots due to stretching unevenness were noticeably visible, and the film had impaired transparency (Table 5).

(Example 11)

In Example 7, a laminated film was obtained in the same manner as in Example 7, except that the uniaxially stretched laminated film was guided into a tenter, stretched 5.0 times in the film width direction at a temperature of 140°C, and the cast drum speed was adjusted to a thickness of 55 μm. As in Example 8, improved spectral shift properties and small coloration after mounting were obtained (Table 2).

(Example 12)

The laminated film of Example 11 was laminated into two sheets by interposing a single-layer optical adhesive film so that the orientation directions were the same. The laminated product of the obtained laminated film showed a phase difference twice that of Example 11 and had a thickness of about 115 μm. As the number of laminates doubled, the reflectivity also increased and the light cut was improved overall. The spectral shift property showed the same level as Example 11, and as the cut property improved, the overall yellow coloration of the transmitted light tended to become slightly stronger (Table 2).

(Example 13)

In Example 8, a laminated film was obtained in the same manner as in Example 8, except that the stretching ratio in the longitudinal direction was 2.8 times, the stretching ratio in the transverse direction was 4.5 times, and the casting speed was increased by about 1.2 times so that the thickness was equivalent to that in Example 8. In Example 8, the stretching ratio in the longitudinal direction was high, and since the pulsation in the film width after uniaxial stretching was large and the transverse stretching was strong, the stretching unevenness in the longitudinal direction of the film and the accompanying unevenness in the cutoff wavelength were large, but by lowering the stretching ratio in the longitudinal direction, the pulsation in the film width was suppressed, and further, a spectrum shift property equivalent to that in Example 8 could be obtained (Table 3).

(Example 14)

In Example 13, as the thermoplastic resin B, polyethylene terephthalate (PET/SPG21/CHDC4), which is an amorphous resin having a refractive index of 1.55 and has no melting point, and is copolymerized with cyclohexanedicarboxylic acid (CHDC) in an amount of 4 mol% for the dicarboxylic acid component and 21 mol% for the diol component of spiroglycol (SPG), was used, and the extrusion temperature of the thermoplastic resin B was set to 260°C. In addition, a laminated film was obtained in the same manner as in Example 13, except that the preheating temperature in each stretching step was set to 105°C. By changing the composition of the thermoplastic resin B, the laminated film was slightly whitened, and extreme points due to diffuse reflection occurred in the measurement by a goniophotometer. Meanwhile, by improving the glass transition temperature of the thermoplastic resin and making the laminated film have improved heat shrinkage resistance, it was successful in suppressing the change in contrast in the accelerated weather test, and overall, the change in brightness showed the same level as Example 13 (Table 3).

(Example 15)

In Example 14, a laminated film was obtained in the same manner as in Example 14, except that the mixing conditions of the thermoplastic resin B were changed to a discharge amount per screw rotation speed of 0.3. By mixing more vigorously, the whitening confirmed in Example 14 was eliminated, and the extreme points in the angular photometer disappeared. As a result, the suppression of the contrast change in the accelerated weathering test became remarkable, and it became the best at this level (Table 3).

(Example 16)

In Example 15, a laminated film was obtained in the same manner as in Example 15, except that a triazine-based ultraviolet absorber (2,4,6-tris(2-hydroxy-4-hexyloxy-3-methylphenyl)-s-triazine) was added to the thermoplastic resin B so as to be 1.5 wt% of the resin composition constituting the laminated film. Since it has properties superior to the previous benzotriazole-based ultraviolet absorbers in long-wavelength cut properties and excellent compatibility with polyethylene terephthalate resin, it was optimal for both the bleed-out property evaluation and the accelerated light resistance test (Table 3).

(Example 17)

In Example 15, a laminated film was obtained in the same manner as in Example 15, except that a triazine-based ultraviolet absorber (2,4-bis(2-hydroxy-4-butyloxyphenyl)-6-(2,4-bisbutyloxyphenyl)-s-triazine) was added to the thermoplastic resin B so as to be 1.5 wt% of the resin composition constituting the laminated film. Although it had long-wavelength cut properties, the absorption intensity was relatively low and a result inferior to that of Example 16 was obtained, but it had sufficient properties for long-term use (Table 3).

(Example 18)

In Example 15, a laminated film was obtained in the same manner as in Example 15, except that the thiobenzotriazole-based ultraviolet absorber used in Comparative Example 3 was added in an amount of 1.0 wt% to the resin composition constituting the laminated film. The amount of ultraviolet absorber added was small, and a synergistic effect of reflection and absorption was obtained even in the long-wavelength ultraviolet range, and good durability and spectrum shift properties were exhibited (Table 3).

(Example 19)

In Example 16, a laminated film was obtained through a heat treatment process similar to Example 16, except that the stretching process temperature during the width-direction stretching was set to two stages of 110°C/140°C. By suppressing shrinkage in the long-side direction through the step-by-step temperature increase in the stretching process, a uniform phase difference in the width direction was obtained compared to Example 16 (Table 4).

(Example 20)

In Example 19, a laminated film was obtained in the same manner as in Example 19, except that the heat treatment temperature was reduced from 230°C to 180°C. By reducing the heat treatment temperature, a balance of shrinkage force in the longitudinal direction of the laminated film was obtained, and the bowing phenomenon was suppressed, so that a slight uniformity of orientation angle in the width direction was obtained. On the other hand, the shrinkage force was improved due to insufficient heat fixation (Table 4).

(Example 21)

In Example 20, a laminated film was obtained in the same manner as in Example 20, except that an intermediate region of a constant film width was provided at 140°C after the stretching process in the width direction. By providing a high-rigidity constant-temperature intermediate region and dividing the stretching process and the heat treatment process, the shrinkage force in the long direction of the laminated film could be further suppressed, and the effect of uniformizing the orientation angle in the width direction was obtained (Table 4).

(Example 22)

In Example 21, a laminated film was obtained in the same manner as in Example 21, except that a 10% unstretching treatment was additionally performed in the heat treatment process. By unstretching during the heat treatment, a laminated film exhibiting the most uniform phase difference and orientation angle among the examples up to this point was obtained (Table 4).

(Example 23)

A hard coat layer was laminated on one side of the uppermost surface of the laminated film of Example 22. By laminating a hard coat layer having high rigidity, the heat shrinkage force was significantly reduced, and a laminated film was obtained that showed no change after an accelerated weathering test (Table 4).

(Example 24)

In Example 23, polyethylene terephthalate (PET/SPG30) copolymerized with 30 mol% of spiroglycol (SPG), an amorphous resin having a refractive index of 1.55 and no melting point, was used as the thermoplastic resin B, the extrusion temperature of the thermoplastic resin B was set to 260°C, and a laminated film was obtained in the same manner as in Example 23. By using SPG alone, which is a non-oriented component, as the copolymerization component, dimensional stability was added, and a laminated film having higher rigidity than that in Example 23 could be obtained (Table 4).

The laminated film of the present invention has a multilayer laminated structure and has the special feature of cutting light of a specific wavelength band, and therefore, for example, in construction materials and automobiles, it can be used as a window film, in industrial materials, it can be used as a film for laminating steel plates for signboards, and in laser surface processing, it can be used as a light-cutting film, and in electronic devices, it can be used as a process/release film for photolithography materials, an optical film for displays, and in other fields such as food, medicine, and ink, it can be widely used in products requiring ultraviolet ray cutting, as a film for the purpose of suppressing photodegradation of contents. In particular, when linearly polarized light is irradiated, it can exhibit unique spectrum shift properties, and since it does not exhibit long-wavelength ultraviolet ray cutting properties for natural light, it has a particularly strong advantage in uses such as displays using polarizers and polarized sunglasses. Since it has durability against ultraviolet ray, it exhibits a stronger effect in the field of digital signage used outdoors and the field of vehicle-mounted displays.

1: Transmission spectrum X when polarized X-wave is irradiated
2: Transmission spectrum Y when polarized Y wave is examined
3: Transmission spectrum Z
4: In the range of wavelengths from 300 to 900 nm, the region Amax formed by the transmission spectrum X and the transmission spectrum Y
5: Micro-region surrounded by wavelength n[nm] and wavelength n+1[nm]
6: In the range of wavelength 350 to 500 nm, the region Amax formed by the transmission spectrum X and the transmission spectrum Y
7: Wavelength band where the transmittance continuously increases by 20% or more
8: Cutoff wavelength λ

Claims (10)

A laminated film in which a layer A including a thermoplastic resin A and a layer B including a thermoplastic resin B different from the thermoplastic resin A are alternately laminated in 51 or more layers,
When linearly polarized light (X wave) vibrating in the direction of film orientation is irradiated over a wavelength range of 300 nm to 900 nm and the horizontal axis is plotted as wavelength (nm) and the vertical axis as transmittance (%), the resulting transmission spectrum is called the transmission spectrum X.
A laminated film, wherein when linearly polarized light (Y wave) vibrating in a direction perpendicular to the film orientation is irradiated over a wavelength range of 300 nm to 900 nm and the transmission spectrum obtained by plotting the horizontal axis with the wavelength (nm) and the vertical axis with the transmittance (%), the area Amax (nmㆍ%) of the largest area among the areas surrounded by the transmission spectrum X and the transmission spectrum Y is 150≤Amax≤1500. In the first paragraph, at least a part of the largest area among the areas surrounded by the transmission spectrum X and the transmission spectrum Y exists in a wavelength band of 350 nm or more and 500 nm or less,
A laminated film in which the area Amax of Amax _{350 to 500} (nmㆍ％) in a wavelength band of 350 nm to 500 nm is 150≤Amax _{350 to 500} ≤1500. A laminated film in claim 1 or 2, wherein the optical density at a wavelength of 390 nm of the transmission spectrum Z obtained by averaging the transmission spectrum X and the transmission spectrum Y is 1.0 or more. A laminated film in claim 1 or 2, wherein the variation range (λmax-λmin) of the cutoff wavelength λ in a wavelength band of 350 nm to 500 nm of the transmission spectrum X in the long direction of the film is 20 nm or less. A laminated film in claim 1 or 2, wherein the transmittance at a wavelength of 390 nm of the transmission spectrum Z at an incident angle of 60° is 20% or less and the transmittance at a wavelength of 430 nm is 70% or more. A laminated film comprising a benzotriazole-based and/or triazine-based ultraviolet absorber containing a sulfur atom in claim 1 or 2. A laminated film in claim 1 or 2, wherein the average value of the in-plane retardation at three points, that is, the center of the film width direction and the midpoint between the center of the film width direction and both ends of the width direction, is more than 400 nm and less than 5000 nm, and further, the difference between the maximum value and the minimum value of the in-plane retardation at the three points is 10% or less of the average value of the retardation at the three points. A laminated film in claim 1 or 2, wherein the orientation angle at three points, the center of the width direction of the film and the midpoint between the center of the width direction and both ends of the width direction, is 15° or less when the width direction of the film is set to 0°. A laminated film having two or fewer extreme values in a light intensity spectrum obtained by measuring reflected light intensity in a range of 0°≤θ≤40° and 50°≤θ≤90° in a variable angle luminosity measurement in claim 1 or 2 and plotting the horizontal axis as angle (°) and the vertical axis as reflected light intensity. A laminated film having a heat shrinkage force of 250 μN or less in both the X direction and the Y direction in the measurement of heat shrinkage force in the film orientation direction (X direction) and the direction perpendicular to the film orientation direction (Y direction) in claim 1 or 2, and having a temperature increase of 90°C or more in both the X direction and the Y direction, and further having a shrinkage force of 250 μN or less in a temperature range of 90°C or more and 130°C or less.

Images